Spector's attorneys have suggested the incident wounded Clarkson's pride and helped her decide to commit suicide, the Los Angeles Times said Tuesday.
Spector is accused of shooting Clarkson at his Alhambra mansion in 2003, hours after meeting her at the House of Blues where she worked as a hostess.
His trial, which began April 25, is drawing to a close with the prosecution presenting its final rebuttal witnesses.
Bay was called to rebut testimony from defense witness Punkin Pie Laughlin, Clarkson's friend, who told the jury last month the actress was so fragile she broke into tears when the director snubbed her at a party.
The "Pearl Harbor" and "Armageddon" filmmaker said he had cast Clarkson in a commercial nearly a decade ago, but was acquainted with her through auditions and parties.
"She was funny. She was saucy. She had no qualms coming right up to someone," Bay testified, adding if he had ignored her at a party, she probably would have slapped him in the face.