The "B" in Cardi B might stand for "bruise" after she took a serious tumble off a chair during her "Little Miss Drama" tour in Las Vegas Friday night.

Check out the clip -- the "I Like It" singer is in the middle of showing off some sexy moves while performing her "Thotiana" remix when the chair slips out from under her, sending her slamming onto the ground on her behind. The pro she is, Cardi doesn't miss a beat and continues performing while thrusting her hips high into the air.

She doesn't fully ignore the blunder, though -- she cracks a joke, blaming the government! Remember, just a few days ago, she dissed ICE at her opening show -- and the feds clapped back by shading her stripping past.

Cardi also joked about her fall on X after her concert ... quoting a video and claiming it must be A.I. Sorry Cardi -- we know this is real!

Luckily, it appears she was packing plenty of cushion to fall back on -- and this is a clear reminder that what happens in Vegas, doesn't always stay there!