As you can see in the screenshot above, the tweet came in response to a tweet I posted which mentioned Feedly, the news reader service. The person who sent the tweet is the developer of a competing service, and for some weeks now he has been trolling Twitter and spamming people who mention one of his competitors.
I can't tell you exactly how long he's been doing this, but I do know that he's sent out dozens and dozens of tweets this morning alone.
There's been a lot of debate in the indie publishing realm over the past year concerning how authors should promote themselves, and while there's still no complete consensus on proper conduct I am sure that we can agree that sending a vast number of out of the blue tweets like the one above is simply unacceptable.
Please note that I am not singling this guy because he is promoting his service; I am calling him out for spam. I also haven't ever yelled at the authors who have tweeted me out of the blue (nor do I plan to).
This activity is nothing but spamming, and it goes against the very idea of what and how you should promote yourself. A social network exists to talk to other people, while this guy is jumping into conversations and trying to change the subject to himself.
That is vain, self-defeating, and liable to open you up to public ridicule. I would avoid it, and luckily there's a pretty simple rule of thumb that can help prevent this kind of faux pas.
Try to keep the out of the blue tweets as a minority of your Twitter activity, not the near 100% from the example above. If most of your tweets aren't part of real conversations then you're doing something wrong.