Ray J Cracks Kim Kardashian Joke, Freaks Out at Dahmer Tattoo on TMZ After Dark Tour

Ray J's doesn't skimp out on the SKIMS jokes on our "TMZ After Dark" tour ... going into a full facetious meltdown when seeing Kim Kardashian's L.A. store.

The rapper took the helm of the tour bus with DJ Mike T of VOX DJs backing him up Saturday night ... and, he cracked up the riders when passing the store -- screaming and curling up into a ball while making a pun about SKIMS.

As you know ... Ray J and Kim K used to date -- he's the dude from the now infamous sex tape -- and, though he's far removed from the relationship, it seems he still knows how to use his ex for an extra wisecrack here and there.

Ray J also loves to get to know the riders on our tour a bit ... though he may want to stay far away from one he met this weekend -- who showed off a tattoo of notorious serial killer Jeffrey Dahmer.

We never got to the bottom of why she's got The Milwaukee Monster tattooed on her arm ... but, Ray J certainly had no interest in finding out.

As always, there's ton of drinks to go around at each place where the bus stops ... and, Ray J ripped off his shirt at one point -- pretty par for the course when he hosts the tour.

Ray J's one of a few people to host the evening ride through Hollywood ... with Chanel West Coast and Jerry O'Connell jumping up in the past as well. The DJs change as well -- with DJ Trey Money playing music on Friday for the riders.

And, Ray J's got some exciting news ... announcing TMZ's All-Out Brunch Party tour, coming soon.

If you're looking for a late-night ride though, we've got you covered ... 'cause TMZ is doubling the fun on Saturday nights with a second bus for "TMZ After Dark" due to overwhelming demand.