After a sporting event; when your teammate is washing his hair and his eyes are closed, someone sneaks up behind him and checks his oil with their thumb (quickly slips a thumb in his ass), then runs off before he is able to rinse the soap away and identify the clandestine violator
After the game someone gave John a rusty ninja. John was attacked by a rusty ninja after the game. Be careful, there's a rusty ninja in there.
When you get your partner to defecate on you while performing auto-erotic asphyxiation on yourself.
Mike: "Hey Ted, that hooker only charged me 30 dollars for a rusty hutcho last night!"
Ted: "Thats awesome man, where'd you pick her up?"
The act of standing astraddle over another person who is laying on the floor while you pour a beer or other clear beverage down your ass crack, thus allowing it to cascade rustily down into the other person's open mouth.
"Don't kiss that girl! She got a Rusty Waterfall last night!"
The act of pissing on your girlfriends leg while she is in the shower.
girl 1: girl, how'd you get that rash on your leg?
girl 2: Oh this old thing? I was showering last night and my boyfriend gave me a rusty leg.
The Female version of a Rusty Trombone which involves a female getting rimmed while a vibrator is inserted into her vagina mimicking the vibrations of a motorcycle. It is also customary for the giver to push his or her lips together and make motorcycle noises into her anus.
Oh Katie last night David gave me a Rusty Motorcycle ride and it was amazing!
When a girl is licking your ass and you realize that you didn't wipe completely when taking a crap earlier in the day.
She was licking my ass and I gave her the ol' rusty bottlecap. She didn't like it, but she kept going. What a trooper!
When you do analingus while inserting your finger (or appropriate probe-like device) into her menstruating vagina.
Gave the oldbag a one-two followed by the rusty tomato, and it wasn't even in season!!