“I should have decked her.”

The accuser in a wacky diva-on-doctor slapdown at the Upper West Side Trader Joe’s came to that realization after a waste-of-taxpayer-dollars trial ended in an acquittal this week.

Dr. Catherine London — who, it turns out, is the chip-off-the-old-block daughter of famously imperial AIG insurance mogul Maurice “Hank” Greenberg — rushed right online to complain after losing the court battle with an angry opera singer that stemmed from a January scuffle in the crowded grocery store’s frozen-food aisle.

“Well I guess I should have decked her as the judge found her NOT GUILTY!!!!” London, a triathlete as well as an Upper East Side family-practice physician, posted to the discussion forum of beginnertriathlete.com.

“I guess it is ok to hit someone if you feel they invade your personal space . . . wow,” London wrote.

London, who practices at the Iris Cantor Women’s Health Center and has appeared as an expert on the “Joy Behar Show,” CNN and Fox Television, is 0 for 2 in battles with Manhattan opera singer Marcella Caprario.

The first happened in Trader Joe’s, after London’s 13-year-old son somehow got in the way of Caprario’s husband, Bill, as the man reached for the store-brand frozen vegan pad Thai dinners with tofu — his songbird sweetie’s favorite.

By all accounts, an expletive-filled argument ensued and the doctor took a step toward the singer and wound up with a swift slap to her right cheek.

The doctor had the singer arrested for misdemeanor assault.

But when they squared off for Round Two in Manhattan Criminal Court this week, the singer again got the upper hand.

Judge ShawnDya Simpson took just 15 minutes to find Caprario not guilty of all charges.

“You had some pretty angry interactions with your patients in Massachusetts, didn’t you?” Caprario’s defense lawyer, Mark Bederow, had asked London on cross-examination — referring to several complaining postings on Web sites when the doctor worked in Brookline.

Contacted yesterday about the online posts by London’s detractors, Bederow said, “I’m not going to criticize prosecutors for not doing their homework, but knowing what I know about her now and based on her testimony, this is a case that simply never should have been brought.”

laura.italiano@nypost.com

