Ack! sorry! Clarity and understanding are good; where Latin impedes those ideals, then, Latin must be bad.
In literal English,
argumentum ad hominem means "argument to the man". In colloquial English, it means "an attack on the person making the argument, rather than the argument itself". There are many variants of it, but someone who uses any such variant is not arguing with you (in a logical sense) but rather bullying you.
Take the original example in this thread, which was, "he says alcohol is bad, but he is an alcoholic". It is an attack on the person who said that alcohol is bad, not the statement that alcohol is bad. It proves absolutely nothing about the badness or non-badness of alcohol. In that way, then, it is fallacious: it fails to meet the
validity requirement of a logical argument.
In literal English,
post hoc ergo propter hoc means "after the fact, therefore because of the fact". In colloquial English, it means ... well, the same thing.
Emy's examples, after the first one, show this error of
formal fallacy. It is often encountered in the presence of existential quantifiers like "all X" or "for some X".
As an aside, ad-hominem arguments and fallacies are favourite tools of mendacious politicians and sleazy lawyers. Don't be suckered in by them, especially if you see them here in this forum where people who post are actively trying to get you to agree with them. As exemplified by those politicians and lawyers, the rules of debate (and of Debate Club) do
not preclude their use.
Caveat lector -- let the reader beware.