A person who will perform any number of sexual pleasures to anything that "it" (usually a she) finds aesthetically pleasing. It is usually categorized as neither slut nor whore because sluts do it for pleasure and whores do it for money. An omnifuck does it for the pure enjoyment of ruining all that is decent in public.
1: Man, look at Brittany! What a fucking whore hanging around all 3 of those guys! Is she dating ANY of them?
2:She's no whore! She's an omnifuck bro. She did all 3 of them. I watched it on the net last night. She promised me a date next week. I hope she doesn't have crabs.