So how does one figure out what logical fallacy is theirs, assuming they don't debate often?
Well, the same way you get good at doing anything in life: by being aware of and practicing your usage of language. If you argue a lot (in the civil, discussion-based manner), you'll learn yourself how people resort to logical fallacies to "strengthen" their point. All this site does is compile the official definitions.
Logical fallacies are debate crutches. To the trained ear, they are obvious and really cause your argument to flat line. However, they seem to be rather effective at persuading people who are uneducated or close-minded on a topic.
It's not exactly accurate to assign logical fallacies to certain people, but rather assign them to different arguments. For example, the "slippery slope" is applied to the homosexuality and marriage rights debate a lot.
Of course, now that you know them, the next time you and your mate get into an argument and he uses one, you can call him out and effectively gut his point (of course, not disclosing the whole argument on the fallacy's fallacy principle).