My Little Pony: Friendship is Magic - Image #348,998

For people who want to know why JFK is a jelly doughnut it's because during one of his speeches in Berlin

He uttered the famous quote ich bin ein Berliner which translate to I am a citzien of Berlin.

But a Berliner can also mean jelly doughnut in German.

@Duraigo:

I can't help you with JFK, but Dexter can be easily explained.