O.T. Genasis -- In Love With the ... Making It Rain Gun!!

O.T. Genasis can't be bothered with all the energy it takes to manually throw dollar bills at strippers ... so he went and got himself a dollar bill gun ... to fire George Washingtons at 'em!

O.T. hit up the new Los Angeles strip club Ace of Diamonds Monday night where he displayed his device ... which we're gonna go ahead and dub, the Makin' It Rain Ray.

We're told the rapper dropped about $5,000 all told.

He's in love with the CoCo ... and also Diamond and Champagne and Destiny and Missy and Candy ...