ass gnat

Some one who unbeknownst to them is hated by all due to their stupidity, constant ability to be conveniently where you are at any given time, overly available, lacking a personality, a douche, a duck, stage 5 clincher, desperation friends even shun this person. They are like an irritating shadow that just never knows when to go the Fuck home, or die off....even when invited blatantly to do so. This person sucks and is the ass of everyone's joke, the third unwanted wheel and destined to masturbate alone to the sci-fi channel with a pint of cherry Garcia ice cream in their parents house until they are over 40 years old. No one cares, notices or cries when this person dies, disappears or moves away....they celebrate, clap, and smile all day long when this happens. People try to set this person on fire or back over them with vehicles. People's moms are the only friend of an ass gnat. I don't know why but moms love that shit.

a name given to someone who never ceases to annoy me

Very small measurement used by toolmakers & engineers, or roughly .0001 or one ten thousandth of an inch. Actual size may vary between shops, but always much less than a pussy hair. About one tenth of a skosh which is equal to approximately one nudge of the dial.

Note: When specified, generally regarded as smaller than the smallest one can measure or produce, since while most people intuitively understand that a gnat's ass is pretty small, few have actually bothered a gnat to measure one.

A very small amount

perfect, exact, right on the money

An unusually suave female possessed of a kind of amiable alacrity.