Kim was on a yacht with the fam celebrating Kylie Jenner's 25th, and what better way than with a round of shots.

Problem is ... the mom of 4 can't throw it back the way she used to, and she choked like Bill Buckner.

KK laughs it off ... at least it appeared so through the hacking fit. The woman clearly loved it. For the record, none of the others had any problem downing the spirits.

As for anyone watching this video who wants to drag Kim because she can't down a drink ... well, she's on a yacht, and you're not!!!