I've done it, they usually can't get me to the ground, much less before I'd have hit them in the throat, groin, or given a kick to the knee. One was a great fighter too, one of the best I've had the pleasure of sparring. BJJ has its place, but is too focused on staying on the ground for most situations. It teaches manipulating positions, holds/breaks, and great joint manipulation, but it focuses on one person. I won't deny its effective use, and it's not fun to not know it when you're on the ground with a practitioner. As long as one isn't too caught up in it as a self defense style, it can be useful. I see too many people with the mindset that it's a hammer and everything around them is a nail.
As a rule, I leave sport styles behind in terms of self defense. Boxing is a clear one, you don't carry padded gloves to absorb blows to the face. Muay Thai is great, but a lot of the strikes take some conditioning for most people to be able to do effectively. It's a very hard style in terms of impact on the body, and most people won't get as much technical knowledge from it.
"Today is victory over yourself of yesterday; tomorrow is your victory over lesser men." - Miyamoto Musashi
[Insert random irrelevant religious quote here]