"It was out of line," Agassi told ESPN.com on Monday. "It was inappropriate. The night was on fire. We were all having fun. I was trying to be comedic. I only had a split second to make a decision. I went for it and it fell flat. I was trying to get past it, but Pete didn't really let me get past it. He didn't really roll with it. I've texted Pete to ask him if I can apologize in person."
The offending joke? Agassi brought up Sampras' alleged poor tipping habits.
The tennis legends found themselves in an uncomfortable exchange last week during a charity match to benefit the victims of the earthquake in Haiti. The awkward back and forth was heard by thousands in attendance and was clearly rife with tension.
Agassi and Sampras were playing against each other in the doubles match at Indian Wells Tennis Garden in California and were wearing microphones for what was supposed to be a lighthearted affair.
Sampras made a comment about he and partner Roger Federer being ahead on the scoreboard, prompting Agassi to jokingly accuse his rival of being too serious.
Sampras then drew a laugh from the crowd by imitating Agassi's pigeon-toed walk. That's when it got weird.
Agassi laughed then said he was going to mimic Sampras. He turned his pant pockets inside-out and held out his hands and said "I don't have any money...no wait. I got a dollar." It was a reference to an allegation Agassi made in a recent book that Sampras once tipped a valet a single dollar and was overall a bad tipper.
After chuckling, and acknowledging the reference, Sampras fired a serve at Agassi's head when he should have been serving to Agassi's partner, Rafael Nadal.
ESPN reported that the two exchanged words in the locker room and neither showed up at a post-match press conference.
"The joke fell flat and I'm sorry," Agassi said Monday. "My hope was that the night was still enjoyable."