I've gotten 3 Bfs in 5 Lemons races.
1st BF: Not sure why I was Black Flagged. Acknowledged to the corner worker that I saw them pointing to me and came in calm but confused. After checking, they realized they had flagged the wrong car and let me back out.
2nd BF: Incidental contact with another car that didn't hold their line going into a turn and we were both Black Flagged. The other car fessed up that it was their fault and after making sure I was not "amped" up, they let me go back out.
3rd BF: One of Blitzen Benz's drivers was taking a line like they were the only car on the track and had hit our car (with a different driver) earlier in the day. During my stint, I made a conscious effort to avoid them. Going into a corner I was braking as hard as I could (due to them being in front of me) but couldn't avoid getting hit in almost the same way, in the same corner, by the same car! I was mad because if I would have stayed on the gas I would have been in front of him by the time he was taking the corner. We both got Blag Flagged and I came in really hot, but not to the judges. They realized we were not at fault and allowed our car back out BUT not with me driving. We had to change drivers due to my show of anger (again, not to the judges.)
In my opinion, all three BFs where handles as best as they could have been. I truly believe that if you don't drive like an asshole and don't act like an asshole when you come in, you will be treated fairly more often than not.
As a side note, we have since talked to Rusty with the Blitzen Benz team and that driver is no longer on their team due shenanigans like the ones during that race.