The Sky Blues manager slammed the performance as "totally unacceptable" after an injury-time Harry Forrester spot-kick clinched maximum points for the Bees.
He said: "We need to work much harder because that was simply nowhere near good enough. I think everyone needs a rocket after that."
Brentford fought back after going behind in the seventh minute when David McGoldrick sprung the offside trap to run on and fire beneath home goalkeeper Simon Moore.
But Forrester levelled for the hosts just before the break when he raced on to Adam Forshaw's through-ball to slam home from 12 yards. And the midfielder popped up in the box at the death to tease a foul out of Jordan Clarke before sending Coventry goalkeeper Joe Murphy the wrong way from the spot.
Despite battling well throughout, Robins was furious with his side's failure to see the game out, adding: "We were right in it and then threw it away, but we will have to take it on the chin. That doesn't make it easier to take, but the only way we will get through this is to work a lot harder."
