Coun Andy Strangeway posted a photo of East Riding Council chief executive Caroline Lacey, next to deputy leader Jonathan Owen at a cabinet meeting at County Hall, Beverley.
The image, published on his personal website, contained a speech bubble, written by Coun Strangeway but attributed to Coun Owen, which said: "Psst, don’t look now but Strangeway’s taking photos. And by the way do you know you're flashing your legs?”
In an email sent to all councillors, council leader Steve Parnaby branded it a "step too far", advising anyone upset about it to take up the complaint with the council's monitoring officer and head of legal and democratic services.
Coun Parnaby said he had received "several complains and concerns" over the "unacceptable" posting, which he said was "clearly a sexist comment."
He went on: "This comment is not one expected by an elected councillor and would not be condoned in any workplace."
Coun Strangeway is no stranger to controversy, regularly criticising Conservative councillors and officers, on his website.
He had tried to defend himself, posting on Monday: "If such words are sexist many UK Nationals would have been closed down. It is not sexist and they are have been not closed down."
However this afternoon he was forced into an abject apology, saying: "I deeply regret that the satirical photoon I published on 19th September caused a degree of discomfort to ERYC CEO Caroline Lacey.
"I have personally apologised to Mrs Lacey and deleted the offending photoon."
Coun Strangeway told The Yorkshire Post his wife also thought it was inappropriate.
He met with Mrs Lacey this morning who "wasn't happy."
But he insisted: "I do not believe it is sexist. I apologised face to face to Caroline, who asked me to remove the photoons and send the apology to councillors which I have done."