Even on very specialized forums and lists, off-topic posting is not necessarily frowned upon,[1] but a common netiquette convention is to mark a new off-topic posting or email by beginning it with "OT"[2] - for example in a forum discussing the Linux operating system someone might post: "OT: Did anyone else see that giant goose?".
Posting off-topic messages to deliberately aggravate other members is a form of trolling.