Is there a word, phrase or urban saying for people who appears polite and reasonable in real life, but is rude and trolling everything on the internet?
The answer that comes to mind is, unfortunately, rather crude:
- Internet asshole is a slang term. It's probable that not everyone knows this term, but it's pretty much self-explanatory (a person who is an asshole on the internet).
To describe the phenomenon in general and not a specific person, you can talk about the online disinhibition effect. The webcomic Penny Arcade also popularized a term for this effect, though it is again rather crude--you may see people refer to it by the name G.I.F.T.