The act of slapping, hitting or otherwise defacing another mans ass. It is not a sign of disrespect. Bro Slaps are reserved for when another guys wants to congratulate or appreciate another man. Another use for Bro Slaps is when a bunch of guys want to have fun and all try and Bro Slap each other at once. These competitions usually last for as little as five minutes or they can start an all out war.
"Hey i really respect you." (Bro Slap)
"Wow what you just did was really good."(Bro Slap)
"Woah man! You just slapped my ass! That was gay."
"That was a Bro Slap! They are never gay!"
"Ohhhh I understand."