blonde joke microwave

there was a blonde girl that went in a eletric store and said to the man can i buy that tv the man says sorry we dont serve blondes so she goes out and buys a black wig and goes into the electric shop again and says to the man can i buy the tv she says can i buy that tv he says sorry we dont setve blondes she says how did you know i was a blonde he replys becuse its a microwave