Stress is a definite trigger for me. When I was in uni, I had to be careful that I didn't get too stressed at the beginning of the year, otherwise I'd trigger a flare. I managed to get through with only one flare the entire time, which was when I transferred from a small community-type college to the big state school.
Moving to the UK also set me off. It was the pre-move trip that initially set me off(ended up in the ER just a day before I was set to fly to Europe), and have been dealing with the flare for the last two years.
It usually has to be big one-off stressful situations that set me off. I try really hard not to let things get to me in everyday life and work, and find that I'm reasonably successful at this. But managing big life events has been a bit challenging.