When people let their children scream in any public place. Restaurants, malls, stores.
I also really believe that there should be "no-children" sections of restaurants, because it seems like most of the time parents don't make their children behave. At my house it would have been "let the beatings begin!"
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“All his life he tried to be a good person. Many times, however, he failed.
For after all, he was only human. He wasn't a dog.”
― Charles M. Schultz
Warning: The above post may be dripping in sarcasm and full of smartassedness.