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1.
(n) - an inverted or pronated rectum, damaged by anal sex with an unusually thick dick or dildo.

(n) - an anus or rectum that protrudes like a barnacle from the asscrack, usually from rough anal sex
She told him that she liked it rough, so it wasn't his fault that she got a rusty barnacle.

"You know how huge Bob is - don't let him do anal or you'll end up with a rusty barnacle."
by dimebag40 April 09, 2010
 
2.
A drink that was invented by two residents of Chico, California (at the time, they were known only as TRistan The Terrible and K.C. Dawg) in early March of 1999. A true Rusty Barnacle is made with bottom shelf spiced rum (usually Kings Bay) and generic Dr. Pepper flavored soft drink(usually Dr. Skipper), however today, other types of rum and any Dr. Pepper style soft drink is commonly used. The drink is still common in Chico and has appeared in the Oakland, San Jose, Sacramento and San Diego area's. Recently the drink has become popular in Maui as well.
A person who has consumed many rusty barnacles is said to have "barnacle Breath".
I have never been so wasted, I'm never drinking another rusty barnacle in my life, or at least, not until tonight.

Don't be mad at Sullivan for hitting on your girlfriend, he has a bad case of Barnacle breath
by Eleven Toes MacMurphy June 17, 2010