Riff Raff -- I'm Dating Katy Perry ... Kinda ... Don't Let This Girl's Ass Fool You

Katy Perry's got an unlikely new BF -- rapper Riff Raff -- at least that's on Riff Raff's wish list ... because he's SMITTEN after the two went on a date last week ... despite his obvious addiction to other women in thong bikinis.

Raff was out in Miami Tuesday when we asked about his date with the "Dark Horse" singer -- Raff says he took Katy out for the Holy Trinity ... sushi, bowling, and drinks ... and he had a blast.

If Katy's down -- Raff says he'd love to see her again ... maybe next week when she's back in the country.

We're a little surprised though -- Katy's a busty woman ... and from this clip, it's pretty clear Raff's an ass man. You gotta see it.