For me it would be an opium den or a drug-addicts hangout. A brothel or bullfight or FIGHT CLUB. A political rally. A political convention. A gun show. A safari. A locked room filled with snakes all writhing all poisonous. A girl's night out. Shopping with anyone for anything at any time. A slaughter house. A puppy mill. An execution hanging lynching. A gin joint filled with drunks. An ancient roman entertainment of lions eating Christians or slaves fighting to the death. Any battlefront during a war. Watching a firing squad do its job. Being forced to listen to every word of a speech made by someone I cannot stand. Being in the company of unfriendly people. Black Friday out and about anywhere. The site of any massacre especially of children.
That's a dam* long list and if I were to give more time to it it would be longer. Is your list of "dare nots" as long or longer?