1. Clandestinely pluck it out and act like it was never there, then try to shake off the disturbing visual without losing his erection.
2. Do nothing but stare at it like a beacon while simultaneously supressing the urge to laugh and/or cry.
3. Pull out immediately, hands to the heavens, lamenting "Game over man! Game over!"
Jasper: "Oh MAN! She had a stowaway. When I saw that I lost my hard-on faster than your Mom hits her knees."