I suppose we all have some kind of “smell” test. If something seems too ridiculous, we wonder if it’s a joke. I think that everyone has a different point at which they realize that something can’t possibly be serious.
Sarcasm can be particularly difficult to identify, unless someone tells you they are being sarcastic. It’s a tricky balance, as a person who pens such attempts at humor.
Should I tell people I’m not serious? Sometimes I put a note at the end to tell people it’s a joke. But sometimes I want to skate close to the boundry—maybe it’s for real, and maybe it isn’t. Sometimes I want it to be obvious that I’m parodying something. So I make it as outrageous as I can, and still, some people will think I’m serious.
Still, if it says that it’s a joke, it’s hard to credit that someone would think it’s serious.