Following on from my ranking of fruit by order of rudeness I’d like to make a brief addition.
Please take the utmost caution in using the word 'kumquat'.
I predict a controversy very like that one about using the word 'niggardly' (where, as I remember it, someone was hounded out of their job for other people's ignorance). Shout 'kumquat' at people in the street and see what happens. It'd be political correctness gone mad you know.