Hot/sexy/sex worthy male. A guy who you would like to grab, as he goes by, just like you'd grab chinese food at a dim-sum restaurant as it goes by on a cart.
Setting: Street-hotpavement middle of July, sweatiness and skimpy clothing abounds. Characters: You and an amazingly beautiful man who happens to catch you eye. You say "Dim-Sum!" in appreciation of this fact.
A dim rim is when you take a fat shit. Just a meannasty raunchy shit that is sure to leave your asshole absolutely blackened with shit. Then someone eats your ass before you wipe. They eat your dimmed rim. They give you a dim rim.