I don't think I've ever seen a BBEG bard in a campaign before.

Commoner: "Please! My children are so tired!"
Level 20 Bard: "cha cha, again!"

Bards make fantastic villains. They can be the puppetmaster whispering in the ears of leaders to cause wars, or they can be the flashy conqueror who gives a villainous musical number instead of a monologue.
Edit: Give the villain Vicious Mockery, and have them use it liberally. The players will want them dead.
- Also, nothing strikes fear into a party quite like knowing the BBEG has Power Word Kill in their back pocket. No save, no spell attack, no change to interrupt. They just tell one of your party members to die, and the party member keels over dead. Hopefully you have a 9th level spellcaster who has counterspell prepped and is willing to upcast to prevent it.
  It can force the party to come up with some pretty elaborate traps just to bait the PWK prior to the fight. Since you can only use it once per day, the goal is usually to force them into a fight with something sacrificial (like a golem or a troll,) bait them into use the PWK on that creature, then rush in before they can escape.
  
  Username terrifyingly checks out for bard....

So that's what happened here
- So that's where Dragon Quest's Dancing Devils and whatnot come from!

Biggest problem is that Suggestion is a broken spell with the description we get. Even just the example means we can steal anyone's weapon with little effort.

Suddenly that music video makes sense
- This Key and Peele skit shows what it could be like for a party. Who wants to do only downtime activities now?

Power Word: Dance
- Otto already trademarked that one.

RIP DJ Casper

Except one everyone has clapped their hands, the spell ends on them.

She's not the BIGGEST bad, but there's a major villain who's a bard type in Red Hand of Doom. (My players are about to meet her, actually.)

That is the reason why the guy that led the revolution against to old realms was a high-level bard...

The battlecry of the BBEG bard.

My last 2 campaigns have had the same Bard BBEG because bards are just so excellent with their ability to alter the thoughts of other.

Now did you hear about the dancing plague?

I don't get bards. I mean, wizards study magic. Sorcerers are born with innate magical abilities. Clerics channel divine power. But what the heck is the bard actually doing? Is he rocking out (over the course of six seconds) to such an extent that listeners take psychic damage? Is that something music just does in D&D? Like if you're a level 1 commoner, can you literally die if the kids practicing on their guitars in the neighbor's garage are too good (or too bad) at it?
(Edit: Yeah, yeah, "housecats kill more level 1 commoners than bards do". Bards are a menace! Don't try to obfuscate with statistics.)
- If you want a lore answer regarding the realms, music (rhythm and sound) are an alternative use of verbal and somatic components. Bards attend "colleges" to study forms and functions much the same as wizards do. Difference being mode. And yes, a 1st level bard has sufficient magical power (if harnessed precisely) to kill.
  Do keep in mind it takes no small amount of willpower for a bard to cast. Thus is the spellcasting mod charisma.
  
  Maybe it's because I'm a computer programmer with no artistic inclinations, but I find it hard to suspend disbelief about bardic magic. Of course a wizard can cast spells because he read a book, since books are important. But music isn't very important (to me) in real life. I can say "that sounds nice" or even "that sounds exciting/peaceful/happy/sad" but I don't think I would be too bothered if I could never hear music again.
  I was exaggerating for comedic effect in my original post - I'm not trying to give bard players a hard time. But I do wonder: if you're a person for whom bardic magic "makes sense" in a way that makes it easy to suspend disbelief, are you also someone who's artistically inclined? Does music "speak to you" in a sense?

My favourite bard BBEGs were from Mystical Ninja on the Nintendo 64.