It's only because he realizes the gravity of the situation that Stiles is able to get a handle on his mouth and facial expression, eyes flicking between the strangers and their apparent car. When he's certain that nobody but Derek and Dean are looking in his direction, his entire body very abruptly, yet silently, goes into the very picture of what the fuck?. They start to walk the direction that the speakeasy (what the fuck) must be in, while the men in front of them carry their illegal booze that they were apparently transporting.

Yeah, this isn't gonna get any less weird.

"You know, I think now's a good time for us to remember that I am not of legal drinking age. Maybe we should not go into the illegal club with the man with the grease stained shirt while I'm looking like I should be busting show tunes." Everything is whispered, but the last bit is said with enough fervor that he swears he spits a little.