It depends on what you call shitting on a country.
If people wish to learn anything about other countries, you have to give them space to hang themselves. So if you know they are shitting without reason, you can correct them. If they are shitting your country with reason, its not shitting as they are correct.
As for the harsh delivery, its part of the game of being young. Some are able to discuss with just simple words, others are used to use harsh language. Answer them politely and if they see it does not work they will most likely stop. If you start discussing who is provoking or trolling who, it is certainly to go out of control.