A dirt bike, and only a dirt bike, that is ridden by two persons of the same sex. ( male or female in case you are a retarded fuck who thinks there is more than two genders)
Otherwise it is a general for any common rug muncher whether or not they are on a bike
Person A) Hey ! There's a girl on a bike
Pereon B) No ! It's a dyke on a bike
Person A) Ohh ! There's another lesbian, but she's in a car
Person B) She's still a dkye on a bike
Joey: hey Ryan
Ryan:what
Joey: ur mom gay Ryan:no u
*Brian walks in*
Brian:you sissies fighting
Joey: shut up fag
Brian: you asker for it, ur bikes a dyke
* time itself is ruptured as everything is consumed by one implosion that eventually turns everything into a blank abyss as god himself sits astonished*