How about the UT/UF/US/SF skelebros getting the 'you mess with them and I'll kill you' speech from S/O's family and/or friends? :)
UT!Sans: Geez, kid. Your family really knows how to welcome a guy. It threw him off his edge for a few seconds, but he’s quick to return to his easy going attitude. He’ll promise that he’s never going to hurt you. And then do his best to seem like boyfriend material. The next few hours will be filled with jokes and a few puns. He’s quick to figure out everyone’s humor and what will appeal to them. It tires him out but he wants your family/friends to like him.
UT!Papyrus: Why?? Would?? He?? Hurt?? You?? Did he do something wrong that would cause them to believe that he’d do such a thing? He can’t find anything that would make them think that. So he loudly declares that he wouldn’t ever hurt you. He is far too great for violence, and you are far too amazing for anyone to ever hurt. And although his personality might be a tad narcissistic (in a charming and respectful way) your family and friends quickly catches on to the fact that this guy is just amazing. An hour with Papyrus and they’re ready to believe that he wouldn’t ever hurt you.
US!Sans: His reaction is close to Tale Papyrus’, albeit a bit more hurt. Why would he mess with you? Does he come off as a bad person? He does his best to seem like the perfect boyfriend when he spends time with them. Almost coming off as clingy and annoying, and also a little fake. Talking to him about it helps. But I don’t know how anyone could even think that this sweet blueberry would hurt you.
US!Papyrus: Well that’s a little hostile to say to someone the first time you meet them, isn’t it now? He keeps his mask on though, and calmly tells them that he wasn’t planning on hurting you. His social skills are pretty good, and he’ll be making funny one liners and puns through the evening. Keeping you close to show your friends and family that he cares about you. The hostile energi they’re sending out is making his anxiety flare up 10x. But he can deal with it.
UF!Sans: Okay first off, rude. He might be a monster. And he might be pretty scary looking. And GOD KNOWS he ain’t boyfriend material. And he’s also pretty mean and kind of an asshole when you first meet him and… Okay to be honest he wasn’t sure where he was going with that train of thought. He gets their concern, though. And he’s so awkward and stiff when he’s around him because he’s trying okay! He’ll tell them that he isn’t going to hurt you, physically or emotionally. But he’ll still notice how some of them are a little doubtful towards him. He’d be too.
UF!Papyrus: He really really wants them to like him. He knows, of course, that their approval isn’t necessary for him to date you. But he feels like he needs it to go on with this. He’s uncharacteristically polite and assures them that he’d do no such thing. When you both get home he sort of deflates into the couch. He is so tired from thinking about every little action and trying to fit into the human view of a perfect boyfriend.
SF!Sans: Is sort of offended. And that doesn’t mix well. Somehow his brain translates what they said into ‘’We’re not sure that you’re good enough for our friend/family member, and also you probably couldn’t even protect them’’ So he goes all out trying to show how powerful he is. And how magnificent and great he can be. It does more harm than it does good. And you’ll be leaving the gathering sooner than expected because he broke a vase and then offended whoever blamed him for it. Not a great first expression.
SF!Papyrus: He’d be offended if it weren’t for the fact that he looks like someone who could break both your body and soul. After calmly and quietly assuring them that he’s not going to ever harm you, he focuses on acting as non threatening as he can. Keeps an arm around you at all times. One part of it is to show that he’s your boyfriend and you chose him, the other reason is that he needs the physical comfort. His anxiety is through the freaking roof. When you get home he’s so tired that he pulls you onto the bed and falls asleep while holding onto you for dear life.
This is what my mind conjured up instead of letting me sleep. It’s stupid and I don’t know how to write dialogue properly but enjoy
Walking out into your living room, you saw Sans lounging on the couch. He was watching tv and flipping through the channels lazily, not seeming to be interested in anything particular. Deciding to have some fun you creeped up behind him, and threw yourself over the back of the sofa. He folded up with an ’oomph’’ when you landed on him, but quickly adjusted his body around you and pulled you closer.
’’Sans,’’ you said as you snuggled closer to him. ’’I’ve been meaning to ask you something.’’
’’what?,’’ he responded still not looking away from the TV.
’’You can catch stuff with your magic, right? Like if something fell, you’d be able to catch it?’’
He shifted his body until he could look at you and then raised his brows.
’’yeah? depends on the object and the speed and what not. what’re ya asking for?‘’
’’So if I fell’’,- you continued without acknowledging his answer- ’’would you be able to catch me?’’
His brows furrowed even further as he tried to see where you were going with all this.
’’if your life depended on it then probably’’, he said still looking puzzled.
You stood up on the couch, arms out to balance yourself. ’’Good,’’ you said while stepping up on the armrest. He reached a hand out for you but you shooed him away. After swaying for a while you seemed to find your balance. Sans looked at you uneasily.
’’Y/N i don’t know what the hell you’re doing but-
’’TRUST FALL!’’ you cut him off mid sentence, throwing yourself off the couch and onto the floor.
’’Y/N!’’ he yelled while reaching for you.
He was too late, and your body hit the floor with a thud. You rolled around while holding your sides and hip, groaning in agony. Sans just stared at you with a blank face as you laid there, writhing in pain from your own stupid actions. After a while he sighed and held out his hand. A red glow enveloped your body and you felt yourself become weightless. Gently floating upwards, Sans moved his hand closer to himself and the couch, making you follow suit. His magic lifted you over and placed you next to him on the couch, where he took over and wrapped you in a hug.
’’you are so fucking stupid,’’ he said as he wrapped his arms around you. ’’i don’t get how you survived childhood you moron.’’
You craned your neck to look at him.
’’You were supposed to catch me y’know’’
’’next time,’’ he said grumpily while once again keeping his eyes on the TV.
You just huffed in annoyance but couldn’t help the smile forming as you sank deeper into the couch cushions. Your bruises be damned, scaring Sans was kind of fun.