Bottoms Up, Kim!

Jennifer Lopez and Jessica Biel had better watch their, er, backs -- cuz there's a new booty-ful babe on the block -- Kim KardASShian!

Kim was showing off her colossal badonkadonk again on Tushday night outside Koi -- where she was anything butt coy!

Thanks, Kim, for pulling up the rear!

Hot Butts: click to launch