They're reaction to you having to kiss someone else in a game of Spint the Bottle
Eren:
He's eyeing the other person suspiciously and gets super jealous, even though it's a .1 second kiss on the cheek.
Levi:
After you quickly peck the other person on the cheek, he grabs your arm and pulls you into an intense makeout session. Everyone else moves the game to another room.
Armin:
Armin is just flat out scared that this will lead to something else and makes an awkward coughing-squeak noise when you kiss the other person
Jean:
Right as you're leaning in to kiss the other person, Jean intercepts and you end up kissing him on the lips.
Marco:
Marco isn't super worried because he knows you love him. He's got faith in you, and you're loyal.
Erwin:
Like Jean, Erwin intercepts. Except with him it's a little more graphic and everyone leaves the room and bleaches their eyes.
Hanji:
Hanji wasn't even paying attention so she didn't even really know what game was being played.
Mikasa:
Mikasa sits there, visibly jealous. She cringes when you kiss the other person and pulls you into her lap when it's over.
I don't really know why I thought of this. Anyways, yeah.
~Ash