An Essex Police special constable sent a picture of his penis to a female colleague, a misconduct hearing heard.
SC James Parker also admitted sending the woman flirtatious messages via Snapchat and discussing sex acts during a police briefing.
However, the officer, who works in Colchester, denies saying he wanted to "bend her over" while in uniform.
The hearing, at Chelmsford Civic Centre, will decide if his behaviour amounts to gross misconduct.
SC Parker was in uniform at Colchester Police Station when he used messaging service Snapchat to send a picture of his genitalia to his colleague towards the end of last year.
He has admitted telling the woman he wanted to "cop a feel" during a briefing, to which the colleague responded that she had "small hands".
The special constable had been messaging the female colleague for several weeks over social media and believed they had built up a rapport.
In defence, his lawyer said he had received "winky face emojis" in response to some messages and had not realised the other officer had been offended.
The misconduct hearing will decide if SC Parker's behaviour breached the standards of professional behaviour in terms of integrity, discreditable conduct and respect and courtesy.
The hearing continues.