The second commandment will often get interpreted as the “Thou Shalt Not Use Four Letter Words” commandment. However, that may be a bit of a mistake. Except in the case of one particular American invective (the one where you call on God to banish something into eternal torment) the case that Paul makes in Ephesians 4:29 to not “let any unwholesome talk come out of your mouth” is probably not linked to the 2nd commandment. (Rather, it’s probably best to think of that as an 8th commandment issue.) 
The second commandment is about using God’s identity by way of His identifiers. In other words, God doesn’t want His identity used for things He Himself would not do.
We break the second commandment when we tell people things about God that He doesn’t stand behind. God is ultimately faithful, just, and loving. When we say things about Him that detract from those things, we’re breaking the second commandment.
Liz has a gradeschool yearbook that does the same thing. It was early on, maybe 2nd grade. But someone took a pen and vindictively drew mustaches and devil horns on some of the kids that they didn’t like. It messed up their faces and took away from a sense of identifying who they really were back then.
The most common way we break the second commandment today isn’t that we use curse words, but that we misrepresent God. From the heretics who carry those “God hates fags” signs to the heretics who make God out to be a caricatured deadbeat hippie dad who is cool with us doing heroin and sleeping with our boyfriend – it’s all breaking away from a faithful picture of who God is.
But it isn’t all bad news. In fact, the whole reason that this is an important commandment to God’s people is because God has declared us to be His Name-bearers in this world. We get God wrong all the time, but He comes back to us to set us right. He comes to us in Scripture, He comes to us in His Sacraments. He refreshes a sense of who we are. He takes His identity back, dusts off our heresies, and says “This, this is who I am. You can trust this.”
He does that in a special way with the cross. Because the cross is where we see God clearly. You can’t look at the cross and say that “God hates fags” or anyone else, because He loved them so greatly that He died for them. You also can’t look at the cross and think that anything that we do is “just cool” with God because when we look at the cross we have a recognition that what He’s doing there is paying for sin. That’s who God is. That’s what the second commandment is about.
So the next time someone asks you what the second commandment is all about, maybe it’s good enough to draw a picture of the cross and point to that.