I've been told that being heavy-handed with the soy sauce when eating sushi can offend the chef. It overrides the subtle flavour of the sushi.
I also hate it when a friend who wants to share my saucer of soy sauce, mix the wasabi vigorously in the sauce. No no no. I take my wasabi on the side and adjust the amount with whatever I'm eating. Some sushi gets a little bit more than the other.
There is one sauce that I've seen being splashed around on plates liberally here, and that's chilli sauce. Chilli sauce or ketchup in my opinion can totally drown the natural flavour of a dish. I like ketchup myself but I put it sparingly or if I am consciously trying to flavour a particularly tasteless food. (KFC very dry chicken comes to mind).
Boggles the mind on how some of my friend would even need chilli sauce for a spaghetti marinara. Why? Why? Why? Or is it normal to do that and I just didn't know? @.@
p.s I should totally chill, shouldn't I?