I'm in IHOP with some loud group of people who look like they came from a party or club. They are cussing talk so loud you can hear every word they are saying. People need to know how to act in public.

You maybe right, they came from a party/club, probably sport event very happy, excited, with many things to talk, maybe celebrating someone's birthday, promotion, farewell, special guest, who knows. The group characteristics tells me that I should get ready for something louder than normal. Might impossible to tell them to lower the volume bc someone is sleeping next table, wants a quiet dinner, to much noise, dont want to hear group secrets, or other reason. Besides small group area IHOP its a place where u will often experienced similar situations not necessarily from a group. I dont think "how to act in public" is the problem unless the talking is rated R. You might focused in the type of restaurant, the market, hours, way is designed, etc, even some servers are loud when talking with the kitchen. Is hard to recommend you another place that is open 24/7 with similar menu. The best advice i guess is deal with it, enjoy your meal and hope you have a better experience next time.

Tell the manager