Tyga and Kylie Jenner are finally doing it -- all the PDA they want ... during their Mexican turn up for her 18th birthday.
They've got a full fiesta going at Joe Francis' estate ... and a ton of company for the celebration. Kendall Jenner, Hailey Baldwin, Pia Mia and, of course, Joe were all out on the beach on Wednesday.
Interesting, when they brought out the Sea-Doo ... Tyga had no problem riding bitch behind Kylie.
Can't blame the guy.