"Ameba", although I try not to use it, because it's usually not that fair to amebas.
When it comes to insulting someone with one word, I find it most satisfying and meaningful to stick to the basics and not get too highfalutin. That way even a dumb-ass can understand.
Its my first day on here and dont want to get deleted....so,i will refrain from telling.
I usually use 'asshat,' but here recently, I've been leaning toward 'fuckwhistle.'