One reason it's wrong is because God has commanded us not to misuse His name or treat it casually in our speech. One of the Ten Commandments states, "You shall not misuse the name of the Lord your God" (Exodus 20:7).
Why does God say this? The reason is because when we use God's name (or the name of His Son, Jesus Christ) in a casual or profane way, we're showing our disrespect for Him. If someone treated you disrespectfully, you'd probably be upset, or even angry. But when we treat God disrespectfully, we're saying that He isn't important to us, and we don't want anything to do with Him. We are treating Him with contempt -- and that is wrong.
Our speech shows what we're really like on the inside -- and to be frank, your speech shows that God isn't important to you. You say you and your friends "don't really mean anything by it" -- but that's the problem: God doesn't mean anything to you. If He did, you wouldn't use His name so disrespectfully.
My prayer isn't just that you'll stop cursing, however (although I hope you will). My prayer is that you will realize your need to repent and seek God's forgiveness, and turn your life over the Jesus Christ. God loves you, and Christ gave His life for you. The most important decision you will ever make is to give your life to Him.