The mouse in the suit was a thief!
He's being a busker on the street and a guy throws him a coin, and the mouse is so enraged that he feels he deserves so much more that he then proceeds to effectively rob the guy, using the excuse that the guy is holding back! That was so arrogant and amoral of the mouse.
But then later on he gets involved with mouse hookers and gangster bears, so I'm really not surprised at that point.
Why are you here if you haven't seen the movie yet?