Big Phil, it's your own choice, as josepp wrote. You can use any word you like, claiming it to be just letters. You'll be surprised how quickly you can get lonely and hated.

"Froggy" is explicitely insulting, reducing a nation to a dish. Same with using a typical first name, such as "Paddy", thus suggesting "they are all alike". Other labels may or may not be considered offensive, depending on the context, as said before.

To avoid such offenses is a general rule of human behaviour. "P.C." is or was something quite different: rules of language designed to help particular groups of persons (and thus winning their votes etc.), even at the expense of ordinary correctness. I am not in favour of that, to be sure. There are some intermediate cases in which advanced diplomacy is necessary. If you learn that, it's your own advantage.