Tieriaprobably will need to be distracted in order to be affected. Getting him drunk would be amazing. Tieria also holds back like... everything. Ever. He has lots of inhibitions. Of course, there is the issue that, if not held back, he will do things that could land him in the DF jail cell and in big trouble for a while (like hacking the prison computer again, or shooting a certain Trinity), so I'm looking to hopefully find a way to keep him from doing that. Otherwise, he will likely be unaffected. will be getting drunk with Neil (YES!!) and will be hysterical to talk to. Please bother him. Before the drinking festivities, he will probably be really talkative anyway, so, if any characters wanted find out things about him, this would be the time.
Duo may seem uninhibited about a lot of things, but there's a lot he hides. He will like be more fatalistic, or less caring of consequences, like drinking more or being an insane flirt (as in the touchy feely kind). He will also be more willing to take stupid risks, so... rope swing off the observation deck at the beach anyone? I hope there aren't any bungee chords around because that clock tower is mighty tempting. Got a drink or food you want to share? Duo will try it. Crazy activity? He'll be up for it.
Kitty is probably as open as she's gonna get, but she's likely to be a lot flirtier, bolder in her statements, probably more into teasing people about relationships and other things. She likes to fluster people, so be prepared. Also, she'll be more open to trying new things. Drinks, food, activities... go for it.
MOMO will probably be unaffected because I really can't think of anything she doesn't do already that wouldn't be out on her sleeve. So, yeah. Also, Realians are probably resistant to getting drunk, or at least have a very high tolerance, so that probably wouldn't do anything.
Touma might not be the most pleasant. Be prepared for severe bluntness, borderline rudeness, and, well, he's just gonna tell it like it is. Not that he didn't really before, but he'd been learning discretion on this over recent times, so it's all coming out now. Also, go ahead and try talking him into stuff. He'll be open to it.