There's an extremely juvenile satisfaction in naming Amarant "Asshole" in Final Fantasy IX, so he introduces himself as the Flaming Asshole. I remember people suggesting that one should name Aeris "My Balls" as it makes Cloud's lament after her death a lot more funny instead of incredibly lame.
Edit: I always use the default names. The only time I went ahead and did the Amarant renaming was when I didn't save afterwards.