Pretend You're Recovering From An Injury
Just stretch for intervals of time. The rest of the room tapping their knees to the ground, lunging out of control like their quads are made of fucking steel? Dude, put those hands to the ground and stretch it out. Just don't look like you're doing a tired, winded stretch. Instead, get a little bit of a pained look on your face, and keep touching your knee or something to signal you're working through a personal thing.
[Photo via @hilaryhrhoda]