So my question is if it is allowed to tag a person just because you don't like him? Is it allowed to tag someone because of your vendetta or something?
It's not forbidden, but it's not really the best thing to do (unless you like dramas).
The best answer is given here in the LoyceV guide :
Be the bigger man!With great power comes great responsibility (
source unknown). Especially when you're on DefaultTrust (or if you want to be on DefaultTrust in the future), you shouldn't (ab)use that power by leaving (negative) feedback when someone does something you don't like. Your Sent feedback is what others use to judge your judgement.
If someone on the internet is mean to you: boo fucking hoo! Use the Ignore button, and forget about them. So closing the scam threads on early stages or forcing suspicious projects to escrow investments can save a lot of people a lot of money and maybe someone's life as well.
Mods are not perfect judges (no one is perfect). If you meet a stranger on the street and he asks you for 100$ and tells you he will give you 200$ back tomorrow, will you blindly give him the 100$ ? It's the same thing here, and just because it's a crypto-thing doesn't mean you have to give your money away without doing a few basic verifications.