1. Please Help Me
I got one of these today, as a matter of fact. I sent a polite, standard rejection via email and received the following from the author in reply: Thank you for taking the time to look at my query. If you can think of any other agents that might be interested in my book, please let me know or feel free to mention my name to them. Ahem. Now, you may think you're forging a lifelong relationship with someone in the industry through your chummy correspondence, but let me disabuse you of this notion immediately. You are, instead, being extremely rude. You've just asked a complete stranger to do your work for you, not to mention making the assumption that said stranger thinks there's anything about your idea worth passing on, and nothing makes someone not want to help you more than that. Do not do this.
2. Please Love Me
While there's ostensibly nothing wrong with the common courtesy of thanking someone for taking the time to consider your query and get back to you, I would urge you to reconsider. We glance at your email to see if it's anything important, and if all we see is Thanks for the note, we hit Delete and move on, seeing as how there are, without exaggeration, hundreds more queries to get to. You may think sending a thank you note will keep your name fresh in our minds, that we'll say to ourselves, "My, what a charming author, I hope to work with this person one day." I can assure you this is not the case. Quite literally, we hit Delete, move on and forget your name. The sentiment is a kind one but completely unnecessary, and in some cases can even be viewed as a nuisance. Do not do this.
3. Please Kill Me
I bet this is the one you were all expecting to hear about, the angry-author-blowing-off-steam reply, but the truth is I get these very infrequently compared to the above. In fact, I have yet to receive one myself, though I did come across one addressed to my predecessor. It read: Thanks for taking all of two seconds to look at my query. You got the title wrong. Common sense dictates you should never, ever, under any circumstances act like such a complete dickweasel to someone who you may work with one day, but as we've already established, all writers are loons. Also, unlike the thank you notes, when this happens, we do remember your name. And people in the industry talk, my friend. And they love to talk about this very thing. Do not do this. Do not even think about doing this. Accept the rejection and move on to whoever is next on your submissions list. Otherwise you will be labeled a dickweasel for all time.
You'd think all this would go without saying, but apparently it needs to be repeated constantly. So, in the interest of creating a better world for everyone, please feel free to spread the word and link to this entry as you see fit. Your publishers and agents will thank you.