A cootchcanceller is a girl that is performing a cockblock between one of her female friends and a dude that was about to get lucky with her. Sometimes, sex is imminent. The girl`s into you. You`ve executed the perfect pick-up and all systems are a go. Everything`s looking good, and you`re about to leave with her, when for some reason, (jealousy, perhaps), the girl`s best friend appears out of nowhere and stops her from leaving with you. She somehow convinces her that you`re a creep and that it`s better to go home, have a girl`s night and watch re-runs of Dawson`s Creek instead of leaving with you and getting laid. For the dude that was about to get the action, the girl that jumped in and ruined it all was a real cootchcanceller.
John and Sally were just about to leave the party to go have a little sex session. They wanted to try an Ian Phelgming followed by a lobeload. Suddenly, Jane jumped in and had a hissy fit. She insisted that Sally stay at the party to talk about their feelings.
John went home alone to jerk off.
That Jane is a real cootchcanceller.