Oldie but goodie:
A British World War II pilot is reminiscing before school children about his days in the air force.
(Joke best delivered with a good thick English accent)
"In 1942," he says, "the situation was really tough. The Germans had a very strong air force. I remember, " he continues, "one day I was protecting our bombers when suddenly, out of the clouds, these fokkers appeared.
(At this point, several of the children giggle.)
I looked up, and one fokker was right above me. I aimed at him and shot him down. They were swarming. I immediately realized that there was another fokker behind me."
(At this instant the girls in the auditorium start to giggle and boys start to laugh.)
The teacher stands up and says, "I think I should point out that 'Fokker' was the name of the German-Dutch aircraft company"
"That's true," says the pilot, "but these fokkers were flying Messerschmidts."