Kendall Jenner's Birthday Party!!

Kendall Jenner turned 21 with a bang Wednesday night, with a whole bunch of celebs and one of the most inappropriate/hilarious questions to Kylie.

The party started at Catch in WeHo, then moved to Delilah nightclub and almost everyone was there ... Hailey Baldwin, Kylie Jenner, Madison Beer, Big Sean & Jhene Aiko, Will.I.Am, Travis Scott, Vic Mensa, Mr. Brainwash, Scott Disick, Chris Brown, Paris Hilton, Cindy Crawford & Kaya Gerber, Romee Strijd, Kris Jenner & Corey Gamble, Khloe & Kourtney Kardashian & Jonathan Cheban.

No Kim Kardashian sighting -- though it's possible she sneaked in a backdoor -- but back to the point ... listen to the question our photog asks Kylie.