Your ears are ringing
Your mouth is dry
You feel that you disagree strongly with your friend about the matter you have been heatedly discussing with them
You are on your way to have a beer or some sort of food because, let's face it, this is going to take a while.
In America, you know you've fought with a friend when:
Apparently nothing has happened
You have no idea what's going on
Maybe your friend is just tired, but maybe they are being totally weird around you.
You ask your friend if they're ok, and they say "fine," and now you know it's really bad.
You tell all your other friends that your friend is being weird.
Your other friends tell you that your friend thinks it's your fault but they don't want to get into it.
Some of your other friends have to not talk to you out of loyalty to the pissed friend.
Months later, you see your ex-friend out at a bar and they finally get drunk enough to walk up to you and tell you they're pissed, and you sort of talk it out for a second shouting over the music, although you can't really hear, but who cares, and then you awkwardly hug and buy each other drinks and introduce each other to all the strangers in the bar as best friends even though you probably never were.