Giving Obvious Advice About What You'd Do Instead
The first instinct we have when we hear about a friend's problem is to fix it. And if it's a problem that can no longer be fixed, we'll tell them how we would have obviously handled it. Clearly our friends and colleagues aren't just coming to us to vent; they're coming to us for our vast wisdom!
Sure, this can be helpful if the problem is fairly straightforward ("Next time, try adding thyme to the sauce" or "Next time, try calling the other rapper's mom ugly when you have the microphone"), though usually that kind of information is easily obtained elsewhere. Much more often, this comes off as "Here's why your stupid problem would never have happened to me!"
So if someone is upset that their boss keeps making them work unpaid overtime, don't say, "Next time he pulls that, I'd tell him to go fuck himself!" Not only is this shunning actual advice in favor of making yourself look like an assertive badass, but it's also implying that they had no good reason for not doing that the first time. It's the same for the oh-so-common advice people offer as a response to harassment: "If that drunk guy was creeping on you, why didn't you just kick him in the balls?"