My wife bought me an air freshener that was supposed to smell like new car smell. I opened it and hung it in my car on the way to work one morning. It smelled all right, not exactly like new car smell but pleasant enough. I left my car in the parking lot and went in to work and didn't think about it for the rest of my day.
Well when I went out to my car that evening and opened it up I was almost overpowered by the smell. I guess it had just built up in there all day and gone bad somehow. Maybe the air freshener smelled that bad the whole time. I got rid of it immediately and drove home with all the windows down. Unfortunately the smell lingered for weeks. I learned a rough lesson that day.