Since when has waving a red flag in front of a bull sacrifice?
Sacrifice: the surrender or destruction of something prized or desirable for the sake of something considered as having a higher or more pressing claim.
An online identity is surrendered for the sake of getting some laughs, so it's a transaction, and thus, a sacrifice...
If the online identity in question was surrendered in the name of a senseless insult, or the posting of an offensive but otherwise irrelevant image, it would be, as you put it 'waving a flag in front of a bull'.
Either way, few members get banned for waving a flag in front of a bull. There is almost always at least some form of attempt at driving home some sort of point. Even if it appears senseless, most who get banned know what they risk when they make that final post. If they are motivated by anything other than the desire to get banned, it is a sacrifice.