A form-fitting, tank-style, white, ribbed undershirt worn by a gay male.
When worn by a heterosexual male, it is referred to as a "wife beater".
"Cy drove his Saab down to Target wearing only his jeans and a bitch slapper."
"Seth got pissed at Winston because Seth had used the last Crest Whitestrip™. Winston beat his ass right there in the half-bath while wearing nothing but his manties and a bitch slapper."