Was he trying to show off?
The other day I was out with some friends and at one stage, one of the guys tried to tackle my friend. At first my friend didn't seem interested, but as soon as he saw me, he suddenly tried to tackle the other guy. No-one else was walking around. Did he change his behaviour because he was trying to show off to me? The fact he changed his behaviour when he spotted me got me intrigued. Any ideas?