Same as penis sympathy.
It's a scene where a man sympathizes the pain another man has felt on their dick.
Mac: Hey look, a guy's trying to grind that long rail.
Denis: He's grinding...grinding...OH SHIT HE FELL AND HIT HIS DICK RIGHT ON!
Larq: Oooh! *feels dick sympathy* I ain't gona be able to have sex for couple of days after seeing that.