Slapping the Hand that Tips

Yesterday was terribly slow. I made one third of my normal Friday amount. I was lucky enough to have a few tables of very nice, very well tipping families. Today it's bartending til 6 and serving til 2am. A part of me hopes it will be busy, but I am working with the manager that doesn't help out at all and is oblivious to what is going on (see my post on falling during a shift).
I am trying a new approach on fighting fatigue during my long shifts. It worked beautifully yesterday. Instead of hitting the coffee pot like a fiend all day I drank water. I also stayed away from the fried food we serve and opted for peanut butter and cashews most of the day. My energy level was high and I was able to sleep well, unlike when I use coffee to stay awake.
Other than staying awake I have another issue to deal with. There is a regular at the Sports Bar that has been making little comments and making gestures (some very obscene) at me since I started there. It has recently crossed a line. Yesterday when I took a break and left the bar the customer told another customer I had left to "take care of business" because I don't have a boyfriend. When I heard this I was shocked. On another occasion this same customer passed behind me and grabbed me by the waist, holding on to me. I was so shocked at the touch I didn't say anything at the time.
Saturdays this customer and I are alone in the bar for about 45 minutes before anyone else shows up. I know I have to do something today, but I have to be very careful. He is a customer and very friendly with the owners. Why can't some guys just take a hint? He's in his 50's, married and has children. I have heard that the other girls at work have had similar problems with him but they solved it by fighting with him. I don't want to go that route.