It varies from time to time with me. I try my best to be respectful to anyone and everyone and just have fun, and seems how most tend to dislike taunting and consider it as disrespectful (in most cases) I just don't do it. Chances are if I do end up taunting they may take it the wrong way, cause they simply have no way of knowing I mean it in a good way nor a bad way sadly.
It's cause of this I refrain from taunting unless someone does a "Taunt Greeting" at the start of the match first to which I return the favor, or someone else taunts whether it's after they win or after a KO. Basically, if they taunt then I don't see the harm in doing it.
It can be very rare for me to taunt just to taunt or to even taunt to be a jerk, but there are some instances where I will do so. For example, I absolutely hate passive players. The ones who only wait for you to approach so they can punish anything you do. The ones who make no efforts to attack at all until you get near them, but otherwise just kind of sit there. I taunt these specific people in hopes of getting them aggressive. I'll taunt without getting a KO or anything just to get them to do something than be passive.
It rarely works though, but I still try in hopes of making them want to bash my face in rather than be all "No no, after you!"
Now, if it's someone who taunts after everything...? Oh yes, I will start taunting right back at them. Most of these guys who taunt after everything are just severely cocky and think they're tough players. You can taunt after a good KO, but to taunt anything and everything is over doing it. It shows that you're cocky if you have to taunt everything, so I won't be afraid to repay that behavior.
It makes these over-taunters furious sometimes when you do it back at them, which I find hilarious. An example of this would be a match between
Me (As King Dedede) Vs a Donkey Kong player. He'd taunt excessively while I was practicing as Villager who I've only been actively playing for a little over a month now and would win a few of the matches. Last match he taunted twice after one KO, so I busted out my main and shown him where that cockiness lands him.
He didn't like that much...
So in short, I tend to use them wisely or at least respectfully, unless someone down right deserves them. I play Sm4sh to just have fun after all and when someone chooses to make it less fun then well, the gloves come off and the hammer comes down.