A Manhattan architect who designs for celebrities including Calvin Klein is trying to turn the tables on a former office manager who is suing him for racial discrimination — claiming the ex-staffer is anti-gay.

Architect Peter Marino, who is accused of using the n-word at his Midtown office, says in a new filing that Deirdre O’Brien called a male co-worker “a big homo,” and used her work e-mail to send “explicit pornographic images.”