"I thought we let go of the rope in the second half," Barbee said.
The Commodores used a 20-2 run during a seven-minute stretch midway through the second half Saturday in a 77-60 win over the Tigers at the Auburn Arena.
After showing signs of life during a four-game stretch that saw it earn its only two league victories, Auburn (9-17, 2-10 SEC) took a step backward in the last week, losing to Ole Miss and Vanderbilt by an average of 24 points.
Barbee was particularly irked Saturday by Auburn's 19 turnovers, the second most it has had in an SEC game. Vanderbilt (20-6, 8-4 SEC) didn't press once during the game, instead allowing the Tigers to hurt themselves.
Even guard Earnest Ross, a rare bright spot with 19 points, 10 rebounds and 5 assists, committed 6 turnovers.
"We just made the worst decisions with the basketball I've ever seen in the second half," Barbee said. "We had guys wide open on backdoors, wide open on post-ups. We had guys who had the ball just taken right out of their hands. Just disappointing."
Even worse, it affected Auburn's defense. After shooting only 36 percent in the first half, Vanderbilt made 60 percent of its shots after the break.
"We started to hang our head and let our lack of offense and our lack of toughness in terms of securing the ball and making great decisions, we let it affect our defense," Barbee said.
A little room was all it took for Vanderbilt guard John Jenkins to shake off a slow start. The sophomore, who leads the league in scoring with 19.8 points per game, struggled early, missing his first five shots.
But, like he did when scoring all 21 of his points in the second half of a victory at Georgia earlier this week, he found his shooting touch, scoring 16 of his game-high 22 points in the second half. He finished with five of the Commodores' nine 3-pointers.
Jeffery Taylor added 20 points and Brad Tinsley 16 for Vanderbilt, which reached 20 wins for the sixth time under coach Kevin Stallings.
"Those guys are veteran. They don't panic," Barbee said. "They stay to what they do and they made plays and made shots."
Some frustration boiled over for Auburn by the end. Barbee was on his players throughout the second half, but diverted his scorn to the referees after two ticky-tack fouls on Ross and Kenny Gabriel.
He earned a technical and had to be held back by two assistants from storming onto the court to address the refs.
"Coach is always that competitive," said Gabriel, Auburn's only other player in double figures with 13 points. "He likes us to be more physical than the other team. ... It doesn't surprise me that he acted like that. It looked like he was ready to go out there, but I'm glad he didn't."
Auburn returns to action Wednesday at Alabama, starting at 8 p.m. ET.