I know mine by rote up to 12x12 and I can do beyond that fairly quickly in my head. That's only because I teach basic maths. If I didn't use it at work, my mental arithmetic skills would go rusty.
I was bad at mental arithmetic at school and I was also the stupidest student in top-set (higher level) maths. I should've been in a lower set but because I was good at other subjects, they kept me there so I could keep making a bigger fool of myself when answering questions.
_________________
Zombies, zombies will tear us apart...again.