My pet hate is the fact that many Irish placenames have been rendered meaningless by English map makers; so we have the "oily river" which is their tranliteration of the "Áille" river - which means "beautiful" - the opposite of what one might infer from the English name!
And the River Braddon - which means nothing at all..from the river "Bradáin" which means river of salmon.
Or the equally meaningless "Owentocker" river - where the name is derived from the Irish words "Abhain t-socair" meaning the still river.
D