The most infuriating situations for me are when I submit a working patch, and it is ignored. This is, thankfully, very rare. In some cases, the patch leads to a better fix being written by the maintainer or someone else (an example of this for me was when I needed yum to support authenticated repositories; it didn't, so I patched it, posted the patch to the mailing list, and soon after one of the members of the team rewrote it to be more robust and have nicer configuration syntax within a week).