To be honest, almost every UK accent irritates me in some way!
The generic posh southern English accent where they pronounce "no" as "neigh".
The Geordie accent because it sounds like they were trying to be Welsh, but got a bit mixed up.
The westcountry accent in general, grates and annoys.
South Wales accent, quite short and harsh, is annoying unless it's being sung, not spoken.
Scottish accents, not the worst, but Glasgow has a bit of grate to it.
Scouse. Enough said.
Brum. Enough said.
Northern Ireland, the way they pronounce "row" as "roy".
In the British Isles, the only accent I really like is that from around Dublin.