OHO standing for One/ Handed/ Operator/...this is basically a short term used for describing the famous but usually unnoticed actions of using a pissing terminal (urinal) one handedly while using your other hand for various tasks such as texting, making phone calls, holding a beverage and/or drinking from it, and such simple things as scratching your head.
Guy1: Dude are you seriously texting while doing that?
Guy2: Well yeah whats wrong with that?
Guy1: Well thats realy wierd bro.
Guy2: Naww very common im just an OHO