Once, when we were working on a hardware proposal, one of my co-workers came to me with a piece of paper with "Onkyo" written on it. He asked me what I thought of that manufacturer. Thinking it was related to our proposal, I offhandedly said "they make consumer-grade stereo gear", with my tone of voice making it clear that I meant this derisively.
Later I found out that he'd just spent a few thousand dollars on an Onkyo stereo system, and he wanted my real opinion on his purchase. Unfortunately for him, he got it.