Colchester made a flying start thanks to hapless Oldham defender Ellis Plummer, who slid the ball into his own net after eight minutes when trying to clear Craig Eastmond's left-wing cross.
Plummer, on loan from Manchester City, was again at fault for Colchester's second goal after 32 minutes as he allowed Dominic Vose to set up Jabo Ibehre for a simple tap-in.
A furious Johnson said: "I feel let down by the lack of desire, lack of energy and lack of will to win.
"It's my worst day in football for a Lee Johnson side to go out and play like that.
"Nothing of my personality was shown out there and I apologise to the fans.
"We were immature and weak. It's difficult when you are missing key players but, come on, these are professional footballers who have to want it.
"I had players before the game saying they were knackered, but that was mental instead of physical and it shows you aren't a winner.
"If players are going to show that level of energy and desire, I will shake it up and transfer-list people if I have to - I don't care who they are."
One player already heading for the Boundary Park exit is Dutch winger Sidney Schmeltz, just six months into a two-year contract.
Johnson said: "It hasn't worked out with Sidney and we are going to talk to him. It might be better for him and for us if we part company."
- Sports & Recreation
- Craig Eastmond
- Lee Johnson