I used to burn and cut my forearms and biceps and triceps. During this time period, I wore hoodies every day, even in summer, so it was hardly ever noticed. The few times anyone saw...well, nobody bothered asking, they knew they'd not get an answer anyway.

I also used to punch and slap my face, but I so rarely saw anyone for several hours after I'd do it, by the time I saw someone any swelling would go down. I gave myself a black eye once, and blamed it on a box falling on me from a shelf.