3
I see the potential but I think you could rework it to make it funnier. The setup makes the punchline obvious and personally I like to be surprised.
I feel the rhythm of how you deliver the joke is funny. Also I’d reword the second half to “The store owner said it’s just a fucking rock”
Make it personal "I hate pawn shops. This guy just tried to sell me a sex stone... all I got was this fucking rock"