annuisance
When someone or something is so extremely aggravating that it's just not enough to call them an annoyance or a nuisance, so you use a portmanteau of both.
Jeff: My little brother is getting on my damn nerves, he's so annoying.
Mark: My sister is even worse, she's the literal definition of annuisance.
Mark: My sister is even worse, she's the literal definition of annuisance.