1. Liquid that comes out of the penis when a male ejaculates. (semen
More precisely, however, it is the residue left inside of a condom after someone is done having sex.
ie: Any leftover cum that is not used for the specific purpose of inducing pregnancy.
The term is derived from "wasted fuck", because the semen was not used for its primal purpose of making a baby.
2. A derogatory term for a jerk or a stupid person. (see synonyms douche
This indicates uselessness, because as you can tell from defenition number 1, "fuckwaste" is something that has no point in being there, so this easily translates into an insult.
Haha I just threw my used condom onto Billy's head, and now he's got my fuckwaste all over his hair!
I just masturbated, now I gotta wash off all this fuckwaste from my hands and pants.
Did you see that fuckwaste lunch lady? She only gave me half a serving of french fries!
You're adopted and your parents don't love you, you fuckwaste!