What makes people think it's okay to touch someone in a inappropriate way? Always ask permission, respect a no. And cosplayers, don't be scared of saying no if something makes you uncomfortable.
I went to Phoenix Fan Fusion recently dressed as a Lethal Company intern. I heard someone yell behind me and when I turned around, I saw a random kid in full tactical gear bum rush me in human crab stature. Idk why but my first instinct was to point at him like in the game and it deterred him and caused him to shriek. I had to turn around and point at him a few more times before he gave up and I got around the corner. Still no clue how to feel about it.