Teenagers can be selfish. And they can be twats. Sometimes they're selfish twats.
Its meant to be this way. I don't know why, but I do know that all teenagers go through phases of this. It can also turn from selfish twattery to funny and interesting at the drop of a hat.
Just wipe the slate clean, have a giggle and get on with the rest of the job. Make a cuppa.
Remember you were a teenager once. And you probably had moments of being selfish. And being a twat. And being a selfish twat. You turned out ok tho!