pestilent

Someone or something that is very annoying, something you can't seem to get rid of.

Pestilent things could be a rat constantly chewing your wires or living in your basement, or a fat seal who won't get off the rock you like.

Damn that guy Omar keeps messaging me. He is so pestilent. Keeps asking me to zorbing with him but I really don't want to. What a pestilent prick.