Francisco Sandaza scored the only goal of the game, in which Peterhead had five players booked and Rory McAllister became the sixth player to be sent-off against Rangers this season.
McAllister was dismissed on a second yellow card for handball midway through the second-half against the Third Division leaders.
McCoist said: "I think the physicality has been taken out the game too much, so I'm not going to be hypocritical and complain about some of the tough tackling our players receive. We're all big boys, so let's get on with it.
"I think after the first game of the season, the guys had to toughen up. They're certainly handling it better and the results we've had recently are based on a solidity and resilience, especially defensively."
Peterhead boss Jim McInally was upbeat despite seeing McAllister sent off and his side subsequently beaten.
McInally said: "I was disappointed we didn't finish the game with eleven men. I substituted Ryan McCann to save him from getting sent off and within five minutes we're down to 10 men.
"Losing Rory was a massive loss to us at that stage of the game. I think it happens a lot where there are wee handballs and the referee turns a blind eye to it."