Generally speaking, an old, wrinkly, long-lobed, snow white haired person that drives way too slow in the left lane, that's oblivious to all else around him or her.
Jesus Christ, look at that foofoofnik driving so slow, they can't evensee over their steering wheel!
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!