There is nothing more gross than taking a big bite out of a wormy mango; there is nothing more distasteful and it always seems to happen to me.
Worms seem to be a big problem in mangoes, and it's impossible to tell from outside which are going to be the wormy ones I never bite into them though. Once I've peeled one, I slice off pieces until there's very little fruit left on the seed. If there's still no signs of a worm, I'll bite off what's left. But if I see any signs of a worm, I'll probably throw out the whole mango. It's really annoying, because mangoes aren't cheap.
Going slightly off topic, I once found a mango seed which was already starting to develop a root before I cut into the fruit. I planted it and now have a little mango tree growing in a pot. I doubt it will ever get big enough to bear fruit, but it doesn't really matter. At least it was a pleasant surprise for a change.