Why did all the dumb jokes go from being about Polish people to blondes?

[RobertR]

When I was a kid all the dumb jokes were about Polish people and not blondes. All the dumb jokes are about blondes now and I never hear one where Polish people are the punchline. Why and when did this happen?

 

[Jeff]

Polish people got sick of it so they started telling blonde jokes.

 

[BUSTER]

there was an intelligence test the blonde's lost