I try not to get in this situation--I bring plenty of my own stuff to smoke and would usually bring a gifted stick home for later. (Even in the case of something really great--delayed gratification.) People are rarely pushy if you show that you appreciate the gesture and promise to smoke it later. I also mostly hang out with guys who smoke good cigars, so when I've been gifted cigars at a lounge in the moment, they've been sticks I'm familiar with, even if I've never tried them.
That said, if really pushed to it, I would give it my best so as not to offend. For my palate there are very few things out there that are truly disgusting and unsmokeable. Something might not be my cup of tea, but it's not likely to make me gag.