Kylie Jenner 18 and So Wet

8/10/2015 8:02 AM PDT

Kylie Jenner -- 18 and So Wet (PHOTO)

This is how Tyga celebrates Kylie Jenner's 18th birthday ... now 100% guilt-free.

KJ's man put up this pic of her dripping wet -- in a dress -- with the caption, "Happy bday to the dopest girl ever!"

No one is toasting this day harder than Tyga.