When your partner gives you a blowjob with a mouth-full of chewing tobacco. This term was first popularized by the Youtubers - McNasty, Soup, TheDoo, and Blarg.
Hey man did you hear Dave got a Sloppy Dallas last night?
No way really?!
Yeah, but the only downside is that he got dip clippings all over his shaft.
That's nasty.
Right before the female is about to give fellatio to a man, she fills her mouth full of dip, giving the man a rough, southern-state look on his shaft post-ejaculation.
The ol' lady back home gave me a Sloppy Dallas right before I went out with the guys yesterday. Shit was itching all night brother.