An essential expression to note if you plan on staying on the internetz for more than 10 minutes. Used under, but by no means limited to 2 main cirumstances:
1. To express a situation in which can be handled by pros, only.
2. To display high regard for something, be it an object or an act of proness etc.
1. Noob: "0h hai, h0wz d0 i fly me a b0at?"
Pro: "umm, pros only tbh."
2. Jihad 1: "z0mgz t0okz out h3li with pistol kthx"
Jihad 2: "pros only"
Pro S Only also known as PSO, Pro Skillers Only are a RuneScape clan. Unlike normal Runescape clans who check to see if you meet stats requirements, PSO instead check if you are telling the truth about your gender. Mainly through the use of your IP address and Email. This is as a result of their ginger leader showing his dick to a guy (thinking it was a girl) in the past and getting scammed for his RuneScape bank.
Recruit : Hey I would like to join Pro S Only, how do I go about getting invited?
Herpaderpus (leader) : Hey recruit, please meet me at GE, we will first do a check to see if your in-game gender matches your real life gender.