Justin Bieber with Stanley Cup -- Blackhawks Fans PISSED ... Because It's the Cup

Justin Bieber is bringing sports fans together ... IN OUTRAGE -- because he dared to pose with Lord Stanley's trophy in the Chicago Blackhawks locker room!!!

A 'Hawks exec tweeted the pic last night of JB touching the Stanley Cup -- arguably the most revered trophy in sports -- with a customized Bieber jersey in the background.

The response was immediate ... and angry:
- If I see one more picture of bieber touching the cup I might just cut my own jugular #embarrassing

- And this is why I will kick the crap out of Justin Bieber! You do not touch the cup! You don't deserve to touch it!

- Bieber takin a pic w the cup and gettin a personalized blackhawks jersey is complete garbage. Where did your bruins flat brim go?

That last one refers to the night we spotted Bieber in a Boston Bruins cap ... right before they started playing the Blackhawks in the Stanley Cup Finals.