Just be prepared for the following types of players:
1. Squeakers - Kids on school holiday who will swear, impregnate your mother, kill your dog, eat your smarties and all sorts of other nasty business (if you believe what they say anyway).
2. Smurfs - Pro/very good players who play with a low rank/no rank - they ultimately destroy you.
3. Trolls - people who swear, insult everywhere, blast music through the in-game chat perpetually, shoot you int he back, give away your team's position, quit the game halfway through...just a true joy to be around.
4. The superserious - Dedicated to the game, sleep with a USP under their pillow, go to the shops with a vest and a flashbang ready to roll. They take the game very seriously and get very upset if you screw up.
5. Gen - he has so many Smurf accounts you will not be sure if you are playing against him or not. One round plays like a Supreme, next round let's the silver leak through. Can ace against Silvers but can't do 10 damage to a DMG.
Also, if you're female, enjoy the attention...