It is difficult for me to ascertain when the person I am communicating is using a logical fallacy to trick me into believing him or doubting my judgement, even when I realise it hours after the argument.
I have seen countless arguments in Reddit threads and I couldn't figure out who was in the right or wrong unless I looked at the upvote counts. Even if the person is uttering a blatant lie, they somehow make it sound in a way that is completely believable to me. If it weren't for those people that could exactly point out the irrationality behind these arguments, my mind would have been lobotomised long ago.
I do want to learn these critical thinking skills but I don't know where to begin from. I could have all these tips and strategies memorised in theory, but they would be essentially useless if I am not able to think properly or remember them at the heat of the moment.
There could be many situations I could be unprepared for, like when the other person brings up a fact or statistic to support their claim and I have no way to verify it at the moment, or when someone I know personally to be wise or well-informed bring up about such fallacies, perhaps about a topic they are not well-versed with or misinformed of by some other unreliable source, and I don't know whether to believe them or myself.
Could someone help me in this? I find this skill of distinguishing fallacies from facts to be an extremely important thing to have in this age of misinformation and would really wish to learn it well if possible. Maybe I could take inspiration from how you came about learning these critical thinking skills by your own.
Edit: I do not blindly trust the upvote count in a comment thread to determine who is right or wrong. It just helps me inform that the original opinion is not inherently acceptable by everyone. It is up to me decide who is actually correct or not, which I can do at my leisure unlike in a live conversation with someone where I don't get the time to think rationally about what the other person is saying.
No true Scotsman is a fallacy, more specifically ad hoc while defending a generalisation about a group defined by another criterion. Easier shown with an example:
If we accept the definition of vegetarian that you implied (someone who doesn't eat meat), "not eating cheese" is at most a generalisation. As such, when Alice says "Those who eat cheese are not true vegetarians", she is incurring in the fallacy.
The slippery slope is an interesting case, because it's both a fallacy and a social phenomenon. And evoking the social phenomenon doesn't automatically mean that you're using the fallacy.
As a fallacy, it's failure to acknowledge that the confidence in the conclusion is smaller than the confidence in the premises - so if you're chaining lots of premises, your trust in the conclusion will degrade to nothing. Here's a simple example of that:
So if A happens, what's the likelihood of G also happening? It is not 90%, but (90%)⁶ = 53%. Even with rather good confidence in the premises, the conclusion is a coin flip. (Incidentally, a similar reasoning can be used to back up Ockham's Razor.)
As a social phenomenon, however, the slippery slope is simply an observed pattern: if a group, entity or individual does something, it's/they're likely to do something similar but not necessarily identical in the future. That covers your example with fascists.
The reason why appeal to authority is a fallacy (more specifically, a genetic fallacy) is because the truth value of a proposition does not depend on who proposes it. If an expert said that 2+2=5 (NB: natural numbers), it would be still false; and if the village idiot said that 2+2=4, it would be still true.
We can still use authority however, but that requires inductive reasoning (like the one I did for the slippery slope), that is considerably weaker than deductive reasoning. And it can be still contradicted if you manage to back up an opposing claim with either 1) deductive logic, or 2) inductive logic with more trustable premises.