Technically speaking boosting is not against the code of conduct as long as you don’t use a glitch or hack to do it. Meaning you cannot get suspended for doing it. But is it really fair to your fellow gamers?
Jump into a Free for All game on Modern Warfare 2. You might find your game cut short by a nuke. How does that happen in a game of 8 people and a score that goes to 30 kills? Nuke boosters. Kids who sit in a secluded area of the map and allow others to take free kills until the 25 killstreak nuke.
Those who boost do not care about their fellow gamers or the game itself. The game was not created to be abused by methods to raise your rank. We all game to have fun. When you boost, you ruin the game for everyone else.
There is, however, a relatively fun solution. Booster hunting. It is easy to tell early on in a game if someone it boosting. Check the score, if someone has quite a few kills and no deaths its time to hunt. Check out the corners, or other random areas of the map. You might just find a few.
Take your shots, believe me you’ll feel a lot better. It will be even better if they send you an angry message after the game. It may not be an official solution but it sure is a good time.