Well, computers and the internet certainly make people upset from time to time, but in this case, I’ll bet it’s something much more specific.
In this case, it might just be you.
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All upper case
The “problem” may be that you’re typing your message in all upper-case characters. Internet users, particularly those who have been around a while, interpret that as shouting.
Imagine you’re having a conversation in a quiet room with someone who is shouting loudly for no apparent reason, instead of talking normally. You’d get grumpy, too.
All caps as shouting has become deeply ingrained in net etiquette, or “netiquette”. When reading text in all caps, many people internalize that as shouting without even thinking about it, and react accordingly. Regardless of your reasons for doing so, you can’t control their reactions. Even with the best of intentions on your part, they will internalize your words as being SHOUTED AT THEM.
They’re likely to get grumpy.
You may not be doing it on purpose, but I definitely suggest using all caps only for emphasis, or when you’re trying to convey that you are, in fact, shouting.
RFC 1855 – Netiquette Guidelines has a good summary that includes this and many other things to keep in mind as you communicate on the internet.
Whenever I discuss this topic, I hear back from people who use all caps to make their text easier to read. Perhaps they have vision issues, and all caps is a quick and easy solution.
Find another solution.
As I said, your legitimate and benign reason for using all caps does not affect how someone reading your words “hears” them. They will hear you shouting at them.
Most programs today have a variety of solutions, including making the font/typeface larger, increasing the native zoom of your computer’s display, or even switching to high contrast themes that are intended to make things more easily visible for those with issues.
Investigate those alternatives. Avoid all caps.
Unless, of course, you really to mean to shout.