When a man (or woman) has hair on the sides of their head, but not in the middle/on the top. Usually because of hair loss, but sometimes because of bad hair cuts, or football season and/or camp.
Becca: Dude, check out that man. EPIC opposite mohawk going on.
Micaela: HAHA that's hilarious!
John: Dude! Yesterday at football practice, I got attacked by the other guys and a hair clipper! Now I have an opposite mohawk!
Kevin: That sucks bro. Just shave it all off.