They are making out, in a manner the script even goes so far as to call "heated," and Chris is really, really wishing he spent more of his time making out with people he didn't work with so he'd have some kind of frame of reference for this type of thing.

"Check it out, I think you've found a nerd soulmate," Mark whispers loudly, especially for a dude who was home-schooled and likes to bird watch. But Chris obligingly looks across the aisle to the opposing gate and holy crap- there's a Yoda backpack leaning up against the leg of a skinny redhead.