This is a good topic and I love it. 

I'm sure that I'll think of more somewhere down the line, but at the moment, I think that the cringiest thing that I ever remember doing is obsessively Roleplaying in the Warrior Cat and Sonic fandoms as a kid. I'm not bashing people that still into those fandoms by any means, but I was [u]really[/u] into them. It's honestly a miracle that I never became a furry with how much I wanted to be a cat at age ten.