JUSTIN BIEBER might want to put the brakes on his reunion with SELENA GOMEZ . . . at least until he has a chance to slice himself a piece of KESHA.  Because yeah . . . that could totally happen.

--In the new issue of "Rolling Stone", Kesha admits she'd hit that.  To be fair, the magazine brought it up.  But she was pretty quick to respond . . . quote, "Sure.  Wait, is he even legal?  Could I go to jail for this?"

--When the interviewer told her he's 18, Kesha said, quote, "Ok, then I would.  We could go out and buy lottery tickets, vote, play putt-putt golf.  All the things that are legal at the age of 18."  (--Kesha is 25.)

--Kesha also admitted that she smokes pot, but not often . . . because strange things happen.  She said, quote, "I get super weird, so it's not something I do all the time.

--"Sometimes I go into the basement and body-paint, and sometimes I get weirdo-paranoid and hide under the covers.  It's just a bad scene."