Nobody will be able to give you a number..
- I've lost hundreds on hundreds of races I don't even remember I watched
- I will never forget the bet I lost because I mistook the tables and I bet on the wrong horse
- I will never forget a lost bet that came because the jockey was so sure of winning and he just idled near the line and was caught up

It's not always about the money, most of those unforgettable bets are because of the circumstances that led to them.