Jason Arnopp writes a great article aimed at script writers but relevant to writers of any sort (and to all people everywhere who want help, if you want to be picky). I was surprised at the last item, as it seems the most basic, obvious oversight. But Jason says it happens a lot:
8) 'Forget' to thank them
Never forget to thank someone who has given you advice, help and especially script notes. This is possibly the most infuriating thing of all, and there seems to be an epidemic of this behaviour going around. Almost every industry pro I talk to, shares the annoyance at not being thanked for helping people. This now seems to be a 'thing'. Strangers appear in your life, out of the clear blue sky (© Larry David), ask for help/advice/a script read, are given that valuable stuff for free, then fail to even thank the helper. That's downright weird behaviour, which has certainly happened to me a few times now. Why would anyone do that? Besides being supremely irritating and ungracious, it pretty much guarantees that the person will get zero help or advice from me again. Don't burn bridges. Don't spread the epidemic.
I believe him, but with difficulty. Are there really people out there like that? I wouldn't be nice to them for long, that's for sure.