A funny thing happened to me recenty, and I'm surprised it had never happened before.   A friend invited me to a concert at Wrigley Field, only the tickets weren't for Wrigley but for one of those rooftop bleacher sections across the street. Included with the seats came an unlimited buffet and beverages. Included in 'beverages' were several different wines, none of which I recognized. I tried the California chardonnay (it tasted like bubblegum but was drinkable) and the California merlot (it tasted like merlot but was drinkable) and the South American red blend (it tasted like merlot but was drinkable).   Our view of the concert itself was less than ideal - all we could see was the back of the enclosed stage - so our attention drifted until we were talking to the folks around us. A young couple sitting behind us joked that the next time we got up for drinks, we should grab them some beers too. I promised I would, and they promised they would, and before I realized it, one of them handed me a glass of wine.   Actually, she handed me a red plastic keg cup. It was full of red wine and ice. It was sweating, like how a frosty beer sweats on a humid day. I sniffed it and took a sip, the chill masking all flavors but dirt. She said They had the bottle out on the counter. It seemed way too warm, so I had them put it on ice, and then she smiled.   So here's my question regarding etiquette: What do you do when somebody hands you a drink that you're sure you won't be able to choke down? Especially from a well-meaning friend or host? And I don't mean a bad drink; I mean an unthinkably terrible drink.   Keep in mind: the one thing I'd always like to avoid is the dreaded label of wine snob. I suspect that appearing detached and unreasonable isn't a good trait for a guy in the wine business.   I've been at parties where I'm given a lousy glass of wine, and I'm usually able to weasel out of commenting about it. If my host is smiling at me and looking for a response, I'll try to offer a quick, vague yet honest observation like "smells like almonds" or "it's got quite a pinkish orange color for a chardonnay" or "boy, that is sweet, isn't it?" I'm blessed with a terribly short attention span, and it's easy for me to forget where I put my drink and to get back to the gin or bourbon or whatever.   But there, stuck in my seat on the rooftop, I didn't have any other options. Here's what I did: I thanked her for the wine. I mentioned that it's not customary to serve red so cold. I took another sip, gave up on it, and strained the wine into another cup with my fingers. In the process, I spilled a fair amount onto my lap. Soon, I was rescued by my friend, who had arrived with another load of fresh drinks, and by the distractions a concert can offer.   So I pose the question to you again: What do you do when somebody hands you a drink that you're sure you won't be able to choke down?