I have one particular unfulfilled fantasy: I want to have sp.. (OnlyFans)

I have one particular unfulfilled fantasy: I want to have spontaneous sex in an elevator with someone I don't know.  The problem is that I don't know how to get it started. I have clear visions of dropping to my knees for a blow job or bending over and lifting my skirt, but I can’t even imagine how we get to that point.  I don't know what I'd say or do to show my interest and willingness without freaking the guy out.  Any suggestions would be appreciated.