"Pain the neck" is a common phrase used to describe someone or something that is tedious, annoying, or troublesome. However, it is always good to have alternative ways to express the same idea. Here are some synonyms you can use: a nuisance, a bother, a hassle, a thorn in one's side, a burden, a vexation, a pain in the rear, a pain in the butt, a pest, an irritation, an inconvenience, a disturbance, a source of frustration or aggravation, a trial, a tribulation, a headache, or a difficulty. By using these synonyms, you can add variety and nuance to your writing or speech and avoid repetitive language.