Depends on the situation, but, translate "difficult, tiring, boring", I think. As rjcorraya says, it is little vulgar, because there is the word "kusai" you can use without "kusai" it's the same mean.

Mendokusai is usually used when you find something or someone is bothering you, or is being troublesome. Yes, it is mostly used in an insulting manner and can hurt people if used in a wrong way... Hope this helped...^_^