I'm just curious why some humorous posts are allowed and others are closed and deleted (something I thought was considered bad practice).
When funny items are most likely to be closed
If there are more than 1-2 "funny" items on the top 15 questions, I'll vote to close one or more of them, except on Fridays.
While it's good to have fun here, people do come here for help and suggestions, and having a constant stream of useless, offtopic items near the top of the front page can be discouraging, "Huh. I wonder if I came to the right place, and if they can even help me." We should avoid the appearance of clique-ish and/or exclusive behavior, even though there's a pretty strong community underneath meta.
Ok, so how do I be funny?
But if you want to be successful at posting a funny item, you'll need to participate in more of the regular questions to get a good understanding of the community, and to get people to know you a little bit. Once you believe you have a good rapport with others here, try something funny late Friday afternoon, when such things are most likely to be accepted. See what the community reaction is, and figure out why it did or didn't work. If nothing else, you'll generally get lots of feedback.
I guess it depends on the community. You need 5 people to close it; if 5 are willing to do so it will get closed.
Personally I think many (but not all) of the joke posts aren't funny and are getting quite old, and I usually downvote them and sometimes even vote to close as off topic. Sometimes other people agree and they do get closed; most of the time they get upvoted, but I'm fine with that: as the FAQ says the website is ran by the community