Adam is pretty prone to crankiness. Garth is a morning person by default, so it’s less likely to happen to him.
who worries more when the other is sick/hurt
Garth is too pragmatic for it, and he’s a very good tender. Adam gets antsy and jittery when one of his loved ones is hurt, so everyone around him gets snapped at. Post-Traumatic Lucien Disorder.
who plays pranks on the other
Adam plays pranks on Garth sometimes just to laugh uproariously at that withering deadpan look that Garth gives him when he realises he’s being punk’d. But it backfires horribly when, say, Garth puts Knothole Island itching powder in his shorts as retaliation.
who is always the first to suggest cuddling on the sofa
Adam. Garth isn’t outwardly demonstrative that often, but one of the signs of his fondness for someone is his willingness to adapt to their demonstrativeness. He puts up with Adam’s occasional bouts of ridiculous affection.
who insists on creating nicknames for the other
Adam calls everyone by seemingly-derisive nicknames – some of his more popular ones for Garth are Glowworm, Smarty-Shorts, Sourpuss, and of course, Old Man Garth (which is shared with Hammer). (In a modern-day Earth AU, “Spark Plug”, “Gandalf”, “Nightlight”, and “Morgan Freeman” are among the more popular ones.)
who drools on the other when they’re asleep
Adam is one of those people that starfishes (you know, sprawls all over the bed) and sometimes lets out a real loud snore or five, so I’d expect it of him. Garth sleeps like the dead until he starts dreaming.
who says ‘I love you’ first
Adam. Garth says it in other ways long before, but he’s not quick to the actual words.