The worse conditions you've play under?
Too Windy - Bugs in your face - Distracting Noise - Cracks on the Court - Darkness - Rain - Cold - Extreme Heat - Shoes falling apart - balls from adjoining courts interrupting play too often - Tennis partner too weak or too strong - Partner talking on their cell phone while you wait - having to wait for a court - bad tennis balls
Those are just a sample of what I've dealt with over the years and I'm sure you have as well.
What other stress invoking situations have you encountered?