A Russian obscene word "уёбок" which means "retarded fucker". There are plenty of synonyms for this particular term, but "уёбок" is one of the most offensive. Use it in casual dialogue, and you'll be punched in the face almost for sure.
A hardo is a person who tries extremely hard at everything. Most times a hardo will try very hard at things that do not require excessive effort. For example, sports practices, gym class, etc.
Wow did you see Jack at practice today? What a hardo!