I'm going to tell my friend to stop talking shit so loudly about the bartender (a friend of mine) when we're at a bar
Are there other reasons why you don't want her to talk about the bartender?
I don't want the bartender to feel uncomfortable around me.
Your friend is so loud and boisterous, but those types of people are the most honest. Being too honest can hinder a relationship with someone else if they are being obnoxious at the same time, so it is best to keep her quiet. She will get you kicked out of that bar if she continues to be so rude.
The bartender doesn't have thick enough skin to deal with my friend.
Then your friend will most likely get kicked out.