Everything you say tells the listener(s) multiple things about you. With a simple sentence, you reveal not only the content of your words, but a host of other information.
Consider the sentence: “I have an extra pen if you need one.” Okay, the literal meaning is that you have an extra pen. But you’re revealing that you think the other person might need one – so you think they’ll have cause to use a pen, and you think there’s some possibility they aren’t prepared for that. You’re saying that you consider your relationship such that you’d give them a pen if they needed it, too. You’re also stating that you’re an extra-prepared person in general, and probably a helpful one, too. Of course, maybe you’re communicating that you’re specifically more fastidious than the other person? And hey, you’re also communicating that you think it’s okay to speak to them!
I could go on. But all this is to say – there are about a million ways even a simple sentence like that could be misconstrued. One lesson here is “choose your words carefully,” but let’s be honest – what more could be done with that initial sentence that wouldn’t be absurd? Even if you tried a version like “I don’t mean to imply that I think you’re specifically unprepared, and I also don’t want to seem like I’m trying to one-up you or anything, but I think that in the near future you’re going to have cause to use a writing implement and just in case I’m right and also in case you don’t have one on you for perfectly understandable reasons, I’d be happy to share the extra that I have with you,” then you’re just communicating that you’re neurotic and you think the other person is so utterly sensitive that they’d be offended if you offered anything less. There’s no escaping this trap.
So instead, take this lesson: Give grace, and interpret charitably. Assume good intent. Life will be better.