Something or someone that is funny to ONLY guys. Women would either not get the joke or be offended by it.
Guy #1: Hey I went to the doctor the other day and he asked for a stool, semen, urine and blood sample, so to speed things up I gave him my underwear.
Guy #2: HAHAHAHHAHA that's hilarious!
Guys GF: Ugh, more like Guylarious....