Kylie Jenner Puts on Christina Aguilera Costume to Kiss Christina

Kylie Jenner played dress up by putting on much LESS clothing, and it was all for Christina Aguilera. Sorry, Tyga.

KJ made an encore appearance in her Xtina costume at Aguilera's 36th birthday party Saturday night. Kylie dressed like Christina from her "Dirrty" days of 2002 ... just like she did for Halloween.

Normally, it's a serious faux pas to repeat a costume, but Kylie says Christina made a special request. Plus, they kissed on camera.

No tongue, but we're still good. She should wear this every night, actually.