Pretending to like something you find distasteful will create problems at work. Although you don't want to offend a colleague, it's better to be honest about your impressions. When asked for your opinion, be as tactful as possible. Make one or two pointed remarks designed to improve a bad performance. Even the mildest rebuke will be met with outrage, but it can't be helped. Thin skinned people shouldn't put themselves in a position of rejection. It's not your job to stroke their egos.