The complete and hasty disappearance of nearly all of the normally external, and usually erect, penis which can result from one of many atrocious turnoffs which a female sexual partner is capable of during or immediately prior to intercourse. Turnoffs which a disappenis may result from could include the presumably female partner revealing her penis during foreplay, dispelling flatulence while male is performing oral sex, or asking her male partner "are you in yet?" several minutes after intercourse was actually initiated.
Guy 1: Dude, how'd things go with that babe after you left?
Guy 2: Not well, man. Not well. 5 minutes into it and BAM...a god damned disappenis.
Guy 1: Ouch. What happened?
Guy 2: She said I was gonna have to wear a condom.