Rhotos is a brand of eyedrops that stings like a bitch when applied to the eye. The amount of pain varies user to user, but it is often excruciating to most users. It comes in different "strength" levels, such as cool, ice, artic, etc. They are frequently used by marijuana smokers who wants to clarify their red eyes after getting high.
Smoker 1: Dude, do you have any eyedrops?
Smoker 2: Yeah sure, I got some Rhotos.
Smoker 1: Dudeeee, it hurts like a mah fakka!
Smoker 2: Stop being a pussy and suck it up.