A dissmisive way to describe vaginal, oral or anal RAPE.
Rape is a crime.
The only 'surprise' should be the punishment by law the rapist receives for this crime.
Some examples below:
I surprised sex on her while she was asleep.
I shoved my cock in her mouth as a treat. She gagged and tried to back away.
She thought I was giving it her in her pussy, but I went up her arse and pretended I didn't know the difference.