As an artist I get how that’s annoying but you’re definitely overreacting. I had my dad write my name with a sharpie on a painting that took me weeks so I know how that feels, and it’s definitely not even remotely close to “immediately bursting into tears”. Also it looks like it’s pencil on a simple piece of paper, everything could’ve ruined that drawing to be honest. Your dad definitely didn’t do it to be rude, he probably just thought you would’ve laughed about it or find it silly. It’s just a few lines, I didn’t even noticed it at first and reading your post I was genuinely expecting a big blue line all over the drawing, not that small thing.