After taking a #2 (without wiping), it is the act of riding down someones arm with your bare ass, ie a railslide.
Frank wasn't paying attention and his arm was exposed, so I took advantage of the opportunity and completed the chocolate railslide, effectively wiping my ass with Frank's arm.
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!