A "Poolfrog" is basically a person who chills and takes it easy,a "no-stress" kinda person ,could be a Male or Female. This kinda guy/girl wants to relax, take a deep breath take it slow and just chill out.
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!