I noticed that they were actually talking about a friend of mine
What were they talking about him for? Was it about something he did?
I'm not sure but they were definitely gossiping and laughing about my friend.
That's messed up that they were gossiping about your friend.
I thought about joining them because I had some things to add to their conversation.
I don't think it's wise to gossip. Wouldn't you be upset if people were talking about you behind your back?