The practice of orally pleasuring the anus/rectum of another by using the lips/tongue. The 'rim' being the anus hence the act of 'rimming.' Usually applied to those with a fetish for having their ass stimulated in such a way. Also a term used for somebody who is a typical 'suck-up' or 'brown-nose.'
'Man, could you get your tongue any further up Mr. Johnson's ass? He's not gonna give you a promotion, quit the rimming!'
Inserting a handful of Skittles candy into your anus followed by your girl tossing that salad and rimming your ass good. With each swipe of her velvety tongue, you push a Skittle, or two, into her hungry mouth and say "Taste the rainbow bitch!"