Cats that look like Hitler....

[Crysalis]

wow. i bet you think you're really clever.

You know actually the correct usage in that case is "off-topic" because "off" is a modifier of "topic." similar to "the late-arriving guest" (late is modifying arriving) or "my well-informed friend" (well modifies informed).

let's use it together in a sentence.

"I posted in the off-topic forum."

If I had meant that the post itself was off topic, it would be correct to omit the hyphen. However, I was referring to the post's location, which is in the off-topic forum.

You are my new best friend.