Of the 100-ish brews I've done since starting this fair hobby, I've dumped two. One was intentional, the other only somewhat so.
I dumped my tripel after letting it ride for a year. A month ago it still tasted of DMS and solvent, so down the drain it went.
I had also entertained the idea of dumping a purported Orval clone that tasted WAY too much like a barnyard. But then a bottle exploded and, mercifully, set off a chain reaction of all the other bottles in the case, so my decision was made for me.