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1.
While performing a 69, you proceed to motorboat your partner's anus with your head, thus leaving a distinct smell and/or skid mark across your forehead.
Friend: Man, I love getting dirty halos, they make me feel hole-y!

Me: Damn that's some shit right there. By which I mean on your forehead. You've got shit on your head, bro.

Friend: Word.
by sexybitches58 November 19, 2012
 
2.
The smell that radiates off of a whore. Ususaly caused by resisting to clean mixed with STD's. Like pulling a whole weekend of nonstop Halo whilst stewing in your own masterbation filth and microwaveable foods.
The girl behind me in math class smells like Dirty Halo. She's such a slut.
by Samsgotgame March 12, 2010
 
3.
The shape and hygiene of a woman's lips whilst giving a blow job.
By golly she's got a dirty halo
by The Band HP February 06, 2009