Rhymes with 'stroll', it refers to a style of fishing where a baited line is drawn in front of fish hoping that one will bite. The person doing is a troller.
The analogy to a baited message hoping for bites is obvious.
"Man that gayfag was good"
"i like a gayfag after sex"
"gayfag's are illegal in public places"
"ide like the non-gay fag section please"
"can i get some zig zag's, you mean gayfags?"