O Levels
To perform oral sex, ordinarily fellatio. Pun on the historic British secondary level exam. Twinned with A Levels which are the act of anal sex

Especially used in the escorting world to signify the provider offers fellatio without a condom.
We had some top O Level action, she sucked the spunk right out my dick and didn't spit, swallowing the lot.

Candy is an openminded girl who has passed her O Levels.