Doing these two things is as impolite as not tipping at a sit-down restaurant in the United States. 

It’s hard to know if you’re doing something socially unacceptable when you’re in a foreign country. In the United States, it’s perfectly normal to talk loudly and strike up a conversation with strangers, but this is frowned upon in parts of Europe that are a lot less «friendly» than America. The best way to learn the customs of a country you’re visiting is to do a little research before you go so you don’t offend people.