Well, lots of things are arbitrary and pointless outside of their context. I rarely put square brackets around words when I talk, for example. When I do, people look at me funny. Funnier than usual, I mean.
But here's why people might get offended (I assume this is obvious to Deborah and most of her nine-hundred-odd sisters, but certain elements of the studio audience may not be enlightened, and I hate to let a rhetorical question go unanswered): When you say "Please pass the salt", you're making some arbitrary sounds which will be understood by speakers of English: They'll understand that you want the salt, and because you said "please" they'll understand that you're being nice about it. When you use the right fork, you're making some arbitrary motions which will be understood by speakers (so to speak) of fork ordering: They'll understand that you've taken the time to learn the rules and that you respect them enough not to offend them, either deliberately or through sheer brutish apathy. Here's another one: When you refrain from bogarting the joint, your fellow shiftless idlers will understand that you respect them enough not to, uh, "kill their buzz" or whatever those crazy kids say these days1. If they're the kind of shiftless idlers a man can depend on, they'll appreciate it.
It's all information. It's all arbitrary and it all means something.
1 I've seen several
disquisitions on
marijuana etiquette around here (
Rituals of Marijuana has a few good ones). There are more purely arbitrary examples than the "
bogart" thing.