assuming that crazy here refers to mentally deranged, angry, or insane and not an unpredictable oddball.
Assuming that we are using the word crazy as an adjective that would mean insanse, demented or mentally deranged
When people confuse public spaces for their private living rooms or working space. It is okay people are quiet and type away to the machines, or busy writing. It is terrible when they are loud mouthed and carry conversation across the restaurant rooms or movie halls..
Some workholics tend to argue,woe or debate their customers over the mobile when you are out for a quiet family evening.
There have been times when I walked upto the polluters telling them that their conversation was boring or here's wishing you successful deal.
But the troubleshooter was a fiver year, who looked at a crowd of teenagers, then she marched upto them with most adult look and told them
"It is rude to make so much of noise when you are eating."