My my biggest fail is hard to pick, but I still remember a certain arena match. One person was low and I planned to BoP him to buy time. The other team also had someone low, within execute range. We were going to have a good shot at winning. Then I accidentally put BoP on the warrior, so he couldn't attack, which gave time for his target to get healed up. Meanwhile my other teammate died. One misclick lost the match.
What is your biggest fail?