1.Having sex from behind (slang: doggy style) & without saying anything to the lady you quickly pull out & put it in her anus before she realizes what you're doing.
2. Suprise anal sex with the woman you are Having Intercourse with
Chrissy: "That guy last night gave me a bloody Sneaky Pete !!!"
Jess: "omfg lisa, Nick fuckn Sneaky Pete 'ed me this morning! "