Charisma is the most important stat for a successful Bard, but it kinda sounds like this person is unlikeable and not even a good Bard, so they would probably have bad Charisma. You can always make your character bad at what they are meant to do, but it will probably get old pretty fast when you’re useless in most situations.

I would recommend just not choosing that class. Maybe pick a background that gives you proficiency with a musical instrument, but even then, it’s probably funnier if they can’t even play. Then choose a completely unrelated class that doesn’t care about Charisma. Maybe they’re a Wizard who read about Bard spells and tries their best approximation while singing and playing poorly. Or maybe they’re just a Fighter or a Barbarian who has to learn to fight off haters while continuing to talk shit.

If you do choose to play a Bard, I would just give yourself high Charisma and role play as an insufferable asshole anyway. At least that way you can have some magic that actually works. Or you could forget Charisma and spell casting and lean into something like College of Swords Bard and focus on Dexterity and Constitution. You’d be better off just picking Fighter, but at least this way you could actually cast spells poorly for the joke. You’d just be hamstringing yourself in the long run. Maybe they are a Bard at level 1 just for the basic spells and then start taking levels in something else when the Bard stuff clearly isn’t working