I've seen others discussing how they would change the theme slaughter for the better, and while I agree with limiting it to just one suggestion per person, I also think people should be trying to make better themes. So, here's my list, in no particular order, of surefire ways to get your theme rejected:

• Symbols. We've all seen light, death, and time a dozen times. A waste of a suggestion. Even when you try to integrate it into a larger theme, it rarely works.
• Jokes. While some may find yeet or Area 51 raid amusing as a joke, nobody wants to be forced into making a game focused on it.
• Meta. A theme is meant to be the topic for the LD, not provide additional restrictions to jump around like use an unfamiliar engine or language does. Something like pick 3 themes makes it difficult to judge how well games stick to the theme; while remaster previous project breaks the whole point of the LD: to make a game within a couple of days.
• Proverbs. These are obscure, a pain to interpret, and even more of a pain to implement. How are you even meant to make a game around Bob's your uncle?
• Repeats. I just made a game around your life is currency, so why should I want to do it again? If I liked my previous game, I would just remake it, and if I didn't, I'd be able to improve upon my past experiences, neither of which constitute making a game from scratch.
• Specific. There are numerous problems with find the killer (needle in a haystack). If it were to be selected, you would have to make a game with a mystery, and with a large selection of suspects.
• Imprecise. On the other hand of too specific, it is possible to make ones that are too vague. Take Rube Goldberg's nightmare. Would this be a machine very simple and efficient, or one very complicated that achieves absolutely nothing?
• Nonsense. What on Earth is a peom? Why would I want to make a game around Shirayuki- Rotkäppchen, which Google informs me is an anime?
• Political. This may be more of a personal annoyance, but I prefer to keep my games separate from the woes of real life. I come here for escapism, not more mention of climate change.
• Restrictive. Anything that forces the creator into a particular artistic style, genre, etc. falls under this category. Examples are 16 bit, Minimalism overkill, or dating simulator. Remember that others may be less confident in drawing, coding or writing in a particular way than you are.
• Negatives. A theme should provide inspiration of what to make, not limit what can be created. No guns or platformer games would severely limit what gets made, with many LD participants simply unwilling to make something other than a platformer.

And some more from @alphish: - Feel-bad. Things that are just depressing like there's no hope are going to generally be less fun to rate too many games of in succession. Sure, these themes can be well-handled by a game, but just as themes that restrict the creator to an arts style or genre are bad, these restrict the tone of the game. - Frustration. A game with a horrible control scheme designed specifically to haunt the player could be good, but it won't be when twenty of these are played right after another. I may have reached the top in Getting Over It, but it doesn’t mean I want to have similar experience dozens of times.

While I'm sure that there are some trolls among us who enjoy posting themes they do not believe are good themselves, I feel as if the majority of people are simply unaware how bad many of their themes are.

From @jeremy-ryan: There is a distinction between a good game idea and a good theme idea. No jump platformer could result in a very good game, but I would absolutely not want to play and rate fifty of them.

In general, before submitting a theme, consider if you would like to make two thousand different games on that theme, and rate them all, without it becoming difficult or repetitive. If you can only think of a few games to make fitting your suggestion, how can you expect us to think of unique games?

Finally, good luck on the Ludum Dare.