Santa Gets Lap Dance at Madonna Show, Falls Off Chair

Madonna's on Santa's naughty list this year -- and while he looked totally down to revel in some fun smut at her concert, it ended up costing him with an onstage fall.

The singer brought out a Claus -- classic red suit and all -- during Tuesday night's stop in D.C. for her "Celebration" tour, and it looks like they were attempting to do some kind of edgy lap dance sequence with him and some of her backup dancers.

SC plopped down on a chair, waiting for his treats -- with Madonna standing nearby to monitor the choreography. When the dancer finally mounted him ... they both went tumbling.

Nobody was hurt or anything, but it was a lil' embarrassing ... especially for the jolly man, who should be plenty used to folks on his lap by now.

Funny enough, no one skipped a beat in the moment. The dancer who went down immediately got back to poppin'/lockin' (even from the floor) ... and Madge continued handling mic duties like nothing happened -- all of this while Saint Nick was slowly trying to get up.