The Sharks shipped nine tries as they were eviscerated 67-17 at Franklin's Gardens on Saturday afternoon.
It brought a crushing end to a five-match unbeaten run in the Gallagher Premiership for Sale, who had not lost in the league since November 17.
And Diamond had some strong words for his players after the game.
"It was probably one of the worst days at the office," Diamond said.
"I really did not see that coming, to be honest.
"We weren't right between the ears.
"We got beaten in every area. We got hammered.
"I'm very disappointed, embarrassed actually.
"A bit like the opposite of King Midas, everything we touched turned to s***. It was one of those days.
"The players looked like they didn't know each other and the message at half-time was to try to get four tries for a losing bonus point.
"I'm thoroughly p****d off."