Wasps. I head outside this morning to trim up some bushes so I can paint around a particular area outside of my house, the little stinging buggers are nesting in the bushes... again... So instead of getting something useful done today, I have to spray down the whole area with chemicals, and wait and try again next weekend. At least I have an excuse to goof off for the rest of the day, but I'd rather be getting done what I had planned to do.
Fortunately, this has happened enough times that before I work in this particular area, I always bring a broom handle and whack the bushes a half dozen times to see what's hiding there. Haven't gotten stung yet, thankfully.