The City boss was the first manager for fourteen years to have his side lose at Oakwell and the City boss is determined that with hard work on the training ground, City can improve.
"I don't want to be dis-respectful to Barnsley but this is a game we need to be winning if we want to be successful," Boothroyd said to the CT's Alan Poole.
"The team I picked was good enough to do that but didn't apply ourselves in the manner I've come to expect and that's really annoying.
"It's been a very disappointing end to a disappointing Christmas and New Year period.
"When you work with people on a daily basis, put in the hours, do the work that's required, it's just preparation for the examination at the end of the week. They have had four examinations in the space of nine days and, on the whole we've been nowhere near what I expected.
"We played half a game against QPR and responded well after having a man sent off against Ipswich. But as Barnsley, we were all over the place - we started badly and gave away two really soft goals.
"You don't mind if somebody scores a fantastic goal against you but that was avoidable. Defending second phase situations has been one of our strengths and you just can't give people that amount of room.
"We battled back, although you shouldn't need a slap in the face before you retaliate but in the second half we shot ourselves in the foot again by conceding another goal from a second phase ball that should be meat and drink to us.
"You expect to be conceding that sort of goal in pre-season, not when you've been working on them for five months. That's why I'm so annoyed, because peope don't live up to what you think they can do and I find that really irritating.
"I'll have a think about what I'm going to do with those individuals and that group and we'll get cracking again. And the only way to do that is to work even harder on the training pitch - you can't blame anybody else, you have to look at yourself and what you can do better."
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