@SuperOniichan
No, the punchline is already obvious. This technique has other purposes:
[ul]
[*] It shows you that the character is dumb because he's meant to be, not because the author is (which is incredibly common, sadly). The author has to be aware of how dumb the situation is, or else nobody would point it out. This can also be played straight, such as when someone has a plan (which appears reasonably serious) and the smarter one points out why it's a bad plan. It doesn't have to be funny.
[*] It explains the misunderstanding (if applicable). The dumb guy is obviously doing/saying something dumb. If you didn't understand
why he's doing/saying it, now you do.
[*] It puts things into perspective. For instance you have "normal girl" Hibiki who points out everything. And then there's everybody else pointing out Hibiki's eating prowess.
[*] It can be reversed for laughs, like how nobody bothers commenting on Machio's clothes anymore because they've all gotten used to it (even though it's still absurd).
[*] It's actually surprisingly realistic. If you saw something dumb in real life, you'd probably point it out too.
[/ul]
Actually, "this is a punchline" is more what canned laughter does.
This is a punchline, people are laughing, you should too, because it's funny, that's why they laugh.
... no thanks.