Left/hand right hand brain? make me smrt?

Hey guys, a question that i had been pondering for quite some time now. Im sure everyone knows the “left hand” “right hand” brain thing, where if you write with w/e hand coexides with a half of your brain. And you use that half. If i write with my right hand, and grab the seat with my left… does that make me use both sides of my brain? Since i can do a lot of stuff with my left hand via uni. Also, if such a though, if i the are able to us both hands to grab the seat equaly well or have the ability to choose between either foot forwards… What happens? lol, an odd question but ive never understood

i know that to write with your left hand you use the right side of your brain