Kim Kardashian Is Putting Her Ass Back to Work!

Break's over for Kim Kardashian after her celebrated butt somehow managed to fly under the radar for 3 whole days -- and now she's making sure everyone gets an up-close look!

Kim says she laid off Snapchat at the start of her Mexican vacation with girlfriends, and her kids, but all bets are off ... now that the paps spotted her at Joe Francis' oceanfront mansion in Punta Mita.

Check out the vid ... #FullMoonFever.