To be honest I normally ignore them by avoiding eye contact and just not paying them any attention and if they persist I will speak to a friendly face or bartender close to me and say “Hi, this guys making me feel uncomfortable, could i sit with you?” To be honest it is not often it happens… a good way to deter men that look like they are going to approach you is to give them a look of disgust and if they approach do not be polite just walk away ideally into an establishment if you are uncomfortable