The Bible describes Noah as a Preacher of Righteousness. Everyone in the world community knew Noah was building a Ark. This was not some super secret stealth project built in Area 51.
It was common knowledge and you cant hide the fact youre building a huge vessel. Unlike anything that was ever built. Im sure he got it all, laughter, ridicule, jokes. The people of the time knew. They refused to believe. That is until it was too late. They had plenty of warning. They just chose to ignore it.
Noah's best friend Larry was the one who ridiculed him the most. Bill Cosby covered it.