When a female convinces you that she is on birth control, and not to use a condom. And when the male is about to pull out to ejaculate, the female wraps her legs around the males torso, forcing him to cum inside her. (Most common occurrence in missionary position)
Example 1
"Emilio doesn't seem to like his wife very much,..... The only reason they got married is because he got Penis thigh trapped"
Example 2
"Shit man!" I was banging daves girlfriend last night, and she totally penis fly trapped me! Good thing I was fucking her in the ass!"