Like JTUK I wouldn't normally be one to advocate resigning by email, however, earlier this year I did just that.
My reason at the time was that, we had already had many band discussions covering all the usual issues: volume, song choice, timing etc. It became increasingly obvious that speaking was a waste of time, as nothing seemed to get resolved.
The final straw for me was after selecting and agreeing on three songs each to add to the set list. At the next rehearsal the singer had learnt his three. The guitarist had learnt none. I had learnt all of them.
As talking seemed to be a waste of time, the following day I resigned by email.
In conclusion: If you suspect you are wasting your time, resign by whatever method will get through to them