Not to sound too obvious about it, but in my book "Dangerous Conditions" are pretty much anything beyond my comfort and skill level.
The first time my wife and I took our C&C 37 offshore (to Cuttyhunk Island, in MA), the day after we arrived to us it seemed "Dangerous". Blowing 20-25, 3-5'' seas. Later in the day, the wind died off a bit and we headed out to Martha''s Vineyard. Had we left in the morning as planned we would have had an uncomfortable, nerve wracking trip. The boat would have been fine, I suspect the crew would have been frazzled and prone to poor judgement.
Now, I know the boat (our former boat) can take those conditions and then some. Since that trip I''ve raced in worse than that, and made a passage in worse conditions too. So now, I''d think nothing of taking the new boat out in what a couple of years ago really gave us pause.
When taking the courses for an ASA Bareboat certification, at one point you are asked "What are the safe conditions for boating in your area?" Obviously there are no concrete right or wrong answers, since conditions everywhere vary widely. The RIGHT answer to that question was the worst conditions that you, as the skipper, felt comfortable handling your boat in, no matter what they were.
If you look at the post-mortems on Fastnet 79 & Syd-Hob 98, you''ll see that most (not all) boats took an incredible amount of wind and weather and pulled through. Many that were abandoned came through fine.
Knowing intellectually that sister ships of my new boat have completed the Sydney-Hobart does in no way make me willing to go out in 50 knots of wind...definitely outside of my comfort zone. Even though I know the boat could take it, it doesn''t mean I won''t screw it up.