Argument from Analogy

I find that analogies are nearly useless for argumentation. Either the two situations are identical, or you've now shifted the argument to the ways in which the analogy is wrong, which derails the original point.

Often, it just seems insulting: "X is like Y, and you obviously agree with Y, therefore your failure to accept X means you're stupid".

Analogies can be useful as a pedagogical tool, where the teacher is aware of the limits of the analogy and can focus students on the similarities rather than the differences. As an argumentation tactic, it gets my hackles up whenever I encounter it.

"X [animal] doesn't do Y [activity], therefore Y is bad for you." is one of my favorites.

I remind people they're not a cow/lion/wolf etc.