The "to ride a bicycle" example isn't as bad despite not being parallel: Mary likes hiking; Mary likes swimming; Mary likes to ride a bicycle.

Violating parallel structure isn't inherently problematic though. It is generally meant to convey the same level of importance between the ideas. That's really not the case in the question example a) though. Dragons eating people is certainly not meant to be given the same weight as them being green. I think we need more context for the examples to really say if they're objectionable. The problem is more that they may be separate ideas and should be split into more sentences, but playing on the pseudo-parallel structure can be humorous, giving them similar weight tongue in cheek.

I mean... I'm sure it can be done badly when done accidentally, but the dragon example sounds like it would be intentional.

"Bastard enumeration" is a much more descriptive term for this, not least because there are probably lots of other ways that a series can be out of control. I suspect that the more recent term was only coined because the b-word is considered naughty.

Despite breaking parallelism,most of these sound natural and only a pedant would have a problem with it in informal use.

"... only a pedant would have a problem with them..."

I like Dragons are big, green people eating machines.

I think that even though this answer certainly explains the issues with it, the original construct in the question of "Dragons are big, green, and eat people" still sounds the most idiomatic / least clunky to me. I agree that if you parse it completely literally the last part does equate to "are eat people" which is strange, but I feel that, as with a lot of other constructs in English, readers parsing it the way it's intended rather than to the letter is going to be more common.

Dragons are big, green, and known to eat people.

@Barmar That was close to a "no true Scotsman" fallacy: "it must be OK, because if you object to it, you're a pedant so your view is irrelevant". Strip the name-calling away from that, and there's nothing useful left. The fact remains, though, that after "Dragons are" and the first two adjectives, the reader will expect a third adjective, and that verb "eat" will derail their train of thought.

I think your (1) is the best phrasing. Why could it "be a little hard to read"? Your first "and" helpfully tells the reader that the next item ends the list. The second "and" helpfully tells them that the preceding text is only the first item in an outer list.

@JimL. Or, "Dragons are big, green, and people-eaters."

@RosieF Because the reader might expect another adjective, as in "Dragons are big and green and mean and nasty". It's a minor issue, and it really depends on context.

Please, please, please, if you are writing or updating your resume, watch for these dragons. I understand that in the course of a long bulleted list, the plot can be lost as each individual item sounds best written one way or another, but when read as a whole it can sound utterly ridiculous and detract from the overall impression of you as a candidate. It may not seem important, especially if you are in a field where writing is not part of the job, but if I have five equally qualified candidates, clear communication can become the decision point.

@JohnBollinger That question could be its own post on this site, I'm afraid.

(+1 for the F&S reference :-)

Dragons are big, green, and humanitarian.

I'm inclined to town down-vote this clear and highly helpful self-answer simply because the question-body raised a highly charged question that is not satisfactorily answered here to my mind: "What's wrong with it? … What's the problem?" All of the examples of the error are awkward or irksome, but there is no question of their intent. Prescriptivism aside, if we are to perceive a "problem," surely it would be one that impedes understanding. I'm having a hard time formulating such an example off the top of my head, but I'm sure there could be one, some garden-path situation.

@AndyBonner This is a style question, so it wouldn't make sense to me to put prescriptivism aside. I can't give actionable style advice without prescribing something.