These are comments that I've wanted to leave. It's quite a long list, so I've made it two-level, arranged as forget it, do something else, and try again. I'm still toying with the order. Many reasons apply only to tag wikis or don't apply to tag wikis, so I've split my presentation into two lists.
Questions and answers
- Not a good suggestion
- Your suggestion changes too much from the original post. [this is kind of the fallback case]
- This is not clearly an improvement, let the original poster have his way.
[For style issues, or when an edit is about opinions rather than correcting something that's objectively wrong. This wording could use some improvement.]
- You claim to be fixing a factual error, but the answer was correct. [only for answers]
- Vandalism [covers spam, editing to add insults, editing to delete contents, afdshfdsga, …]
[Should this raise an automatic flag if the user isn't anonymous?]
- Please try again
- This edit is too minor. Please fix more of the obvious issues.
- This edit introduces more issues than it fixes. [should generally be accompanied by a short indication of which is the good stuff and which is the bad stuff]
- Do not use the
edit
button to reply to an answer. [answers only]
- This should have been a separate answer.
- This should have been a comment.
- Please update your question instead. [only if the editor is the asker]
- Please upvote the answer if you liked it, and consider marking it as accepted. [the last bit, only if the editor is the asker]
- Flag to merge user with asker [if the editor is not the same user as the asker but clearly the same person] [no rejection message, but instead raise a flag requesting an account merge]
Tag wikis (excerpts and bodies)
- Not a good suggestion
- This is not an improvement.
- Vandalism [covers spam, editing to add insults, editing to delete contents, afdshfdsga, …]
- Please try again
- Your edit introduces more issues than it fixes. [should generally be accompanied by a short indication of which is the good stuff and which is the bad stuff]
- Your proposed content does not adequately describe the main use(s) of the tag. [a common issue with tags that have different immediate meanings to different crows, such as many TLAs]
- Your proposed content is copied from an external source. Don't do this.
[Technically a subcase of the previous one, but a common one. Usually the external source is Wikipedia, and it's both a license issue and an issue with the selection of information. On SO, suggested tag wikis for products sometimes are ad copy written by the company or project.]
On free-form reasons
At least the “please try again” category, if not all of them, should have an optional free-form field in addition to the canned reason. Ideally, this free-form field should be available when accepting as well (“thanks, but next time please remove ‘thanks’ as well”).
I'm undecided about allowing an “other” category. I can't think of a reject reason that doesn't fit here, and I've rejected something like 800 or 900 suggested edits across Stack Exchange. I haven't trawled through my whole history to write this post though, so it's possible that I've missed something. “Not an improvement” is pretty broad anyway. I think I've covered all the reasons that have been mentioned in this thread so far.
Ancillary remarks
While you're at it, please implement the long-awaited Reject and Improve button.
other
response should be a necessity.