(exclamation): Originating as a greeting by Chief Thunderthud (the only Indian ever to have a moustache) to the Peanut Gallery on the 50's television program "The Howdy Doody Show", the term was later adopted by surfers in the 60's.
(noun): The only place you can take pictures of your hot teenage cousin when she's wearing almost nothing at all, in full view of your family and hers, and not have to worry about getting clobbered for doing so.
Teen boy: Hey, cuz, how 'bout a shot of you in that bikini?
Teen girl: What, are you crazy? Some kind of perv?
Teen boy: How about at the beach, then? A shot of you sitting in the surf!
Teen girl: OK, let's go!
(adj.) Once a man reaches middle age and his formerly remarkable and youthful looks have completely lost their edge, he develops an air of such utter harmlessness that he is no longer attractive to women. A man is described as "avuncular" when he stops looking like a sexual entity and starts looking like his Uncle Arby.
I'll have to stop hitting the clubs looking for action; my face has gotten so avuncular, chicks think I'm there to look for my runaway daughter.