beater
Short for wife beater, and also known as a Guinea-T.  A sleevles white undershirt usually worn on its own by guys trying to show off a muscled up physique.  Although it is usually associated with Italian American men, it has become very popular among many other ethnic and racial groups. The wife beater is a staple of the roid head wardrobe. 
"The weather is getting nice bro, time to bring out the beater"

"I usually work out in a beater"

"I'm trying to get jacked son, so I can rock a beater this summer and flawse for the mamis."