Fun fact: 9/10 users with no linked gamertag are better than you at Halo. That doesn't necessarily mean that I am; but it does mean there's a pretty solid chance.
The fact that I can never pull one together myself. None of my mates play this game any more; I'm lucky to manage a team of 4 for Arena most days, never mind 8.
They're not as much of a problem as a lot of people say they are. I search as a random in BTB a lot (lolnomates) and I rarely come across them more than once or twice a day. The only reason so many people complain is because they want an excuse to use if they're called out on being bad at the game; it's like 'my K/D is low because I'm always getting betrayed'. It's not a valid reason at all, but people try to hide behind it anyway because it's the best they've got.