It's reversible by cutting all your hair off.

( Moon Girl Technologies horrendous beanbag, Mon 19 Mar 2007, 16:05, archived)

or by bathing in fire

( Boondocks, YEAH! has a massive penis. Everyone is scared., Mon 19 Mar 2007, 16:06, archived)

Aye.
But it's pretty irreversible for the hair involved, though.
( Johnny Catfish - Yowsa!, Mon 19 Mar 2007, 16:06, archived)