kill somebody just before he/she earns an 10 or more killstreak
Chat with our AI personalities
Complete the Flawless challenge Survive the entire game see related link
You have to complete the Pavelow III challenge, which I believe is call in 25 Pavelows.
You have to bomb the entire enemy team with a single airstrike. It could be a stealth bomber, which is easier.
There are 3 'weed title's' available in Call of Duty: Modern Warfare 2: Joint Ops: Get 15 assist kills (hurt an enemy player and have a teammate kill him) High Command: Become first prestige, level 45. Blunt Trauma: Get 2 melee kills while you have the Riot Shield equipped. Next to that, you also have a weed emblem: http://images1.wikia.nocookie.net/__cb20091126044537/callofduty/images/4/43/Emblem-weed.jpg To unlock this, you need to complete The Denier challenge.
You have to get invited by a co-host or a host that hosts challenge lobbies