Special Chief Inspector Andy Whitworth, based in the Midlands, pinched the woman while out socialising with colleagues while off-duty in Derby on October 16-17 last year.
The public four-day hearing held in London was also told that on the same night out, Special Sergeant Gary Sims slapped a woman.
Both called to answer allegations relating to breaches of the standards of professional behaviour namely authority, respect and courtesy and discreditable conduct at a misconduct hearing from 5 September 5-8.
The panel concluded that the allegations were proven and amounted to gross misconduct. SCI Andy Whitworth was dismissed without notice.
SPS Sims, from London, resigned from the force following the incident. Had he still been serving, he would have been dismissed without notice.
Detective Superintendent Pete Fulton, Head of British Transport’s Professional Standards Department(BTP), said: “These were two senior officers who abused their positions and subjected two junior colleagues to unwarranted sexualised behaviour on a night out.
“Police officers are expected uphold the law and behave with the utmost integrity whether they are on or off duty, which both Andy Whitworth and Gary Sims failed to do. They do not reflect the values of BTP and I wholeheartedly agree with the decision of the panel to dismiss them both.”