I hold a mouse in my right too. But that's because most mice are designed for right hands.

I'm left handed, and I use a mouse with my right hand since I was 11 (now I'm 35) because my two brothers are right handed.

It's not that simple either though. Yes, I do play the guitar with my right hand and I use computer mice with the right hand. This doesn't change the fact that writing with the right hand is incredibly stressful to my brain and right-handed scissors do not work in my right hand either. Handedness is more like a default setting: You can change the setting to the other hand, but you will have to make an conscious effort to do so every time a new motor skill is learned. I refused to learn computer mice with my left hand because that's just not where mice where in computer rooms and at friend's houses and such. I refused to learn left-handed guitars because then I wouldn't be able to play any other guitar than my own. That's not "doesn't matter" that's "deliberately put in the effort to override the brain".