(Once again, please note that these are my personal pet peeves. It is fine to disagree, but I don't really have much interest in having a dialogue about them.)

(1) The absolute worst:

Awards that are based on voting, to any degree, are popularity contest trash and completely worthless.

(2) The greater offenses:

(a) Not putting whether your contest is (OPEN), (JUDGING/CLOSED), or (COMPLETED) in the title.

(b) Not stating if your contest is only for a very specific kind of entrant in the first sentence of the description.

-For example, if your awards are only for fanfic of a certain band, it's not adequate to title the awards after an album of theirs, as non-fans won't recognize it. You need to state that it is only for (insert band name) fanfic directly.

-Awards that only allow traditional fanfiction (based on movies, books, videogames), but that label themselves as contests for fanfiction, are one of my personal pet peeves. Not specifying that real person fanfiction (based on models, musicians, athletes, actor/actress, etc.) may not participate until several chapters in is incredibly irritating and inconsiderate. Wattpad groups real person fanfiction within the fanfiction genre at present. Thus, a contest for fanfiction can reasonably be assumed to be inclusive of both RPF and traditional fanfic. (Note! I have seen the opposite be the case as well, and that's equally unacceptable.)

(c) Having the title/description of your contest be in one language, but the actual text of your contest in another, is false advertising.

-For example, there is nothing wrong with having a competition only for works in French, but having the contest's title and description be written in Tagalog will only frustrate users who were expecting to be able to enter their Tagalog works, as well as lead French authors to assume they aren't eligible to enter.

(3) Other no-nos:

(a) Don't spread the awards over multiple books. While having separate books for judges, entries, or winners is just fine (and sometimes advantageous to avoid clutter), having the rules/categories in a separate book from where one enters is ridiculous. 

-Note that additional books where you list the winners/etc. would ideally not be in place of listing them on your main book, only supplementary.  The exception would be a long-running contest that is regularly held.

(b) If you require inline comments, it will often obscure the entry form that the applicant needs to fill out, as one may not be able to scroll up and down. This is something I didn't think through adequately for my own contest. 

-Also remember that every time you edit a line, any inline comments that were there will no longer be inline, and will only be at the bottom with general comments.

(c) Don't put the entry form in a chapter other than that which the applicant needs to use it.

(d) When you come up with a name for your contest, don't just use the name of another contest. Come up with something interesting or descriptive.  (e.g., bad name = 'The Summer Awards,' good name = 'The 2017 Blazing Summer Sun Awards')

(e) Don't have categories in your contest that make no sense whatsoever.

-For example, 'Brightest shining diamond.' Unless you clarify that categories like that have certain, concrete characteristics as qualifiers, they're meaningless catch-alls.

(f) Don't have endless chapters. No one wants to sift through 50 chapters to try and figure out if anything important has changed since the contest started. 

-This can be difficult at times.  I was able to get around this to a certain extent by unpublishing (but NOT deleting) chapters which were no longer relevant or useful in any way.  Y

(4) Stupid exclusions:

(a) If you say everyone can enter in the description/initial chapters, you should mean it. Don't then, much later on, go on to specify that random/poetry/fanfiction/mature/etc. are not accepted. By definition, those caveats mean that you do not allow everyone to enter.

(b) There is absolutely nothing wrong with not allowing mature entries. However, specifying that you will allow mature entries with abuse, torture, violence, and expletives, but nothing with sexual content beyond kissing, is totally asinine. If you don't see the problem with that, you are probably a casualty of American culture.

(c) Personally, I don't get why someone would run a contest only for residents of a given country. So long as the works are written in the chosen language, why would it matter? However, if you must do this, make sure it's made obvious in the title and/or description.

(5) Oddities:

(a) The idea of having a category/categories that are designed to recognize accounts (e.g., best fan account, best writer of horror/poetry/5SOS fanfic/whatever) is not a bad one. However, the only really legitimate way to fairly assess an entire account is to read all of that author's works, or be familiar with their contribution to the community concerned in some way. I'm not sure how to implement that kind of award in anything other that a profoundly biased, bullshit fashion. I don't know what kind of legitimate criteria could be used.

(b) I don't get why some contests have random chicks on the cover. Don't do that, it's so, so, so stupid.

(c) I have been surprised to run across quite a few contests that were adamant that they were creating a community with a lasting bond. They often feel that people should not enter because they want to win, but for some loftier reason. Seriously, if someone is looking solely for feedback on her work, and not positive reinforcement, she would be submitting it to review books, not to contests. While it isn't offensive to take that attitude with your contest, it's definitely pretentious.

(6) Sigh:

(a) I felt like I shouldn't need to specify that it's totally awful to have favoritism of one's friends as an element in a contest that involves people other than said friends. But given what I've seen, apparently even that needs to be directly stated. *eyeroll*