I do it a lot when I'm on the phone or when I'm listening to a presentation or anything where I have a piece of paper in front of me really. I think doodles are super fascinating. I never mean to doodle and sometimes I only notice it after I'm already done. They're art created straight by the subcoscious in a way.
Mine are often quite large and have little whitespace left. Big, intertwining blotches with soft curves and neatly filled in lines. I'll see if I can find one to share in the comments.
Mine are almost always a chaotic grid like pattern. Lines perpendicular to each other but of varying lengths. I did an art piece once trying to describe my anxiety/add brain, and it was the closest representation I could get to wanting structure and organization but unable to obtain it.