It's all a question of spelling and culture. Here in the UK an ass is a donkey (sort of hairy horse type thing), so an asshole is a non specifically located hole in an equine beast, or a hole made by same.

An ARSEHOLE, however, is a different kettle of poisson altogether. As an arse is a specific part of the anatomy containing a functional hole used for the disposal of waste products in both solid and vaporous form.

Therefore, you are either as arrogant as a donkey or as a s**t tube. Seems to me neither is anything to shout about!