The Hoops were beaten 3-2 by the Buddies at Hampden Park to be denied a cup final berth and Lennon was furious with his players for putting in a below par performance.
"I am bitterly disappointed with that performance," he said.
"It was soulless, it lacked intensity, desire and will to win, all the attributes this team has shown over the last six to nine months.
"That was an impersonation of a team that I know. There is not one player, maybe with the exception of (Gary) Hooper, that would get pass marks today.
"There was a lack of discipline in our shape and play.
"I thought we were defensively awful, the decision making was poor and the there was a lack of quality in the final third.
"Some of them behaved like spoiled kids out there.
"The treble is gone, we have only ourselves to blame. The criticism is going to come our way and rightly so.
"Hampden seems to be a bogey ground, but to be fair that's the worst we have played here.
"I'd like to congratulate (St Mirren manager) Danny (Lennon) and his team, he is a good guy in the game.
"I don't want to take anything away from them, but I cannot be too enthusiastic about our performance."