It's a word most used by the Venezuelan people, to refer of someone or something as annoying
Tu eres una ladilla!!! You are very annoying..
Ladilla is the spanish word for crab louse. Therefore it's usually used to reflect that someone can be as annoying as a crab louse. It can also be use in the form of a verb "ladillar". For it's sexually related content, it can also be found in expressions with such intention.
"Hombre, eres una ladilla" as in "Boy, you are such a pain", or "deja de ladillar" as in "Quit fooling around".
Something really annoying
que ladilla es maria