remember fighting with a guy who thinks he/she knows everything about realms, reincarnation, multiverse, and maybe more. Apparently this person is a bigot and thinks he/she knows everything. Example: I explain why anything (Even any fiction we know today) can be real under certain reasons and the person said something like: "You can turn anything you want in the realms, or so, but not this or that.." And the person just says that because of the rabid emotional bigotry emotions this person has.

Anyway, I found a really stupid stamp that claims "You were never a -name- in your paste life!" (It did not exactly said that maybe) and it was pretty stupid.
Worst of all it was part of that rabid anti-wolfaboo group; attempting to make people who believes in reincarnation and past lives as another animal as "rabid".

Well sorry to burst your all "knowing" mind bubble, but you do not know anyone's past life.
I wouldn't argue things as "fact" just because I said so, but this is obviously true. YOU DON'T KNOW ANYONE'S PAST LIFE.
The only one who is doing the "because I said so" is the guy who thinks he/she knows the afterlife, the before life, realms, dimensions, multiverse, and maybe more.
It's quite possible that if a past life exist, then it's VERY possible that you were an animal in a past life some time.

Humans are animals too, and no animal on this planet (Including us) has a special difference in our nature.

Now of course, we probably don't even know if we had a past life, but under the theory that we had past lives, you do not know anyone's past life.
And it might be possible for people to remember their own.

Heck, life it's self could be an illusion, and Otherkin too could be possible in spiritual terms.