Makoharu headcanon: when going to super boozey parties, Haru tends to be the sober one; he only lets loose when it’s a party with only the Iwatobi &closer members of Samezuka. Rei and Nagisa, when drunk, are amplified versions of their usual selves, but a lot more touchy-feely.
Makoto is a very happy, giggly drunk and a bit of a lightweight. He coos over cute things and hugs them close because they are “his babies”. Haru can drink a lot and usually drinks most of Mako’s drinks as well as his own, so that the tall boy won’t pass out too early.
When Haru gets drunk, he is (at first) completely still and silent in a poor attempt to veil the fact that he is drunk. As he drinks more he let’s out random bursts of giggles, before returning to his precious serious state. When he is absolutely plastered, Haru gets a serious case of bedroom eyes and lounges around in his unbuttoned shirt and lazily touching various parts of his body, completely oblivious to the hungry stares coming from everyone else in the room. Of course, no one dares do anything because Mako has latched onto his “precious Haru-baby”.