However, it is unethical that you have ruined the reputation of another person in such an act.
I'm still not sure if I believe this story, as it doesn't seem like something a rational, thinking person would do. But assuming what Little Mouse said is true, you're absolutely right. Involving another member in a silly "experiment" like this is inconsiderate at best, and then keeping silent after the other member got tagged by multiple people is reprehensible.
Before experimenting you should have informed RapTarX about the matter and sought his permission. Or someone reputed to the forum should have been informed in advance.
It would have been infinitely better had Little Mouse just not carried out that experiment, because there was nothing to gain or to really learn from it.
If that's what he did, at the very least he should have consulted RapTarX first. LoyceV's suggestion of signing a message in advance is an even better one, because then there's undeniable proof of what the intentions were.
On a related note, I don't think RapTarX's reputation is destroyed exactly. True, he got negged because of this, but I've never considered him a shady character. I'm not even sure I've even looked at his feedback until now. I've got a custom trust list, so his feedback score doesn't show up red, nor does Little Mouse's.
What a fuck up this was.