One of those rare insults, that can and will no matter how you say it, have a very harsh inflection on the word HORSE. try it now say in angry voice " Go fuck a horse "
and horse comes out like you mean it. now say it in a happy voice. Same inflection.

Due to all this awesomeness of the phrase "Go Fuck A Horse " it is considered in part, as the second best inflective insult, after PRICK.