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1.
The guy who always does things that people sarcastically praise with a "YEEAHHHHH!" The guy will often say "YEAH!" himself too. The yeah guy exhibits barbaric characteristics, all of which might coincide with the common definition of a douchebag. The guy does things, such as smash a car window for no apparent reason or douse himself in beer, again, for no apparent reason, purely for the sake of being a chode. When people respond sarcastically with "YEAHHHH," it is an attempt to allude to the ridiculousness and irrationality of the yeah guy's said action.
Ed: Yo Marcus, I just fuckin' punched dat guy in da FUCKIN face in front of his girl.

Marcus: ....YYEAAHHH! THATS A REASONABLE THING TO DO! You're not clearly a yeah guy!

(unaware of the sarcasm, Ed responds)
Ed: YYEAAAHHH, I DON'T GIVE A FUCKKKK!!!!
by StefanLunovuch August 10, 2009
 
2.
The unofficial name for males between the ages of 15-30 who lift the suspension of thier trucks to retared proportions, drive fast, cut people off because they can, speed up through puddles and speed bumps after which they usually yell, "YEAHHHH!". They are unusual in the way because they have many douchebag qualities but have more testosterone than any one person should possess, thus making them harder to classify. Also known as Assholes, they love to look for fights over everything and anything, including a slight look in thier direction, thier girlfriend or even thier trucks. Usually easily spotted from a distance because of the stickers on thier trucks or thier clothes, which consists of everything from Metal Mulisha to Famous Stars and Straps to No Fear and many other companies. These creatures originated in Southern California in Orange and Ventura Counties, but have since spread throughout the rest of the Western United States and as far inland as Texas. They should be approached with caution and possibly avoided at all times.
"That fucking Yeah-Guy just cut me off doing 85!!! Asshole!"
by davethelightguy May 15, 2007
 
3.
The unofficial name for males between the ages of 15-30 who lift the suspension of thier trucks to retarded proportions, drive fast, cut people off because they can, speed up through puddles and speed bumps after which they usually yell, "YEAHHHH!". They are unusual in the way because they have many douchebag qualities but have more testosterone than any one person should possess, thus making them harder to classify. Also known as Assholes, they love to look for fights over everything and anything, including a slight look in thier direction, thier girlfriend or even thier trucks. Usually easily spotted from a distance because of the stickers on thier trucks or thier clothes, which consists of everything from Metal Mulisha to Famous Stars and Straps to No Fear and many other companies. These creatures originated in Southern California in Orange and Ventura Counties, but have since spread throughout the rest of the Western United States and as far inland as Texas. They should be approached with caution and possibly avoided at all times.

"Look at all those stupid trucks. Its like a yeah guy convention."
by davethelightguy June 12, 2007
 
4.
See definition 6 of prolly and mums.
"Am I good at basketball?"
"Yeah guy." (No)
by Whit Smith February 06, 2005
 
5.
that guy at the party who is ALWAYS THERE, you dont really notice him during the party, noone really knows him, but when you look pictures the morning after, he will be there, in the background, smiling with a beer, most likely giving the thumbs up sign.
"dude whos that guy behind you with the thumbs up in this picture?"
"I dont know man, I thought he came with you!"
"HES THE YEAH GUY"
by Luna Wilson January 06, 2008
 
6.
Yeah Guys are the roid munching body builders at the gym, who usually have large tattoos and wear loose singlets, and call out "YEEAHHH!!!" after doing a set of heavy weights.
Yeah guy: (after a set of 20 pullups with additonal weights added); "YEEEEEEEEAHHH, im so awesome!!!"
by jsmitty50 February 02, 2011
 
7.
The Guys at the gym who yell out YEAH! when entering the gym, or after finishing of workout.

These guys normally wear loose singlets, have huge muscles and also many tattoos.

Often friends with trainers and other huge roid raging yeah guys.
Guy 1: Wow, that guys lifting like 150kgs.

Yeah Guys:(after he lifts the weights): YEAAAHHHH!!
by johns11150 February 16, 2011