Gyarados is a large, blue, dragon-like animal hailing from the hit Pokemon gaming series. Recognizable by its serpentine body and constantly opened mouth, Gyarados is a popular choice among male players for its fierce and intimidatding looks.
Gyarados evolves from Magikarp, conversely the weakest of all Pokemon by far. Evolving a Magikarp into a Gyarados is highly worth it, however, as a well-raised one can effectively rape the shit out of many other Pokemon.

The accidental yet embarrassing act of blowing water out of a bong through the slider, soaking the Marijuana. It gets its name because the action closely resembles the Pokemon Gyarados.
It often happens with first time bong users who forget they can't blow out the ash like they can with a bowl or pipe.