All by yourself, at best +13
Reliably with point buy, +8.
Take a variant human Cleric. Put your 15 in Charisma, put one of your two +1 incerases on Charisma, for at total of 16 or +3 bonus. Pick Persuasion as your skill. Pick Skill Expert as your feat (Tasha's Cauldron of Everything) and select Persuasion as your Expertise skill (you also can put another +1 on Charisma, so if you roll for the ability score, and get an 18, you can get to 20 or +5 bonus). For one of your cantrips, pick the Guidance cantrip. Before engaging in Persuasion attempts, pray for divine guidance with it, to get +d4 on your skill check.
This will give you a total of
- +3 to +5 (Charisma ability bonus)
- +2 Profiencincy
- +2 Expertise
- +1 to +4 Guidance
Total in the best case: +13
What's even better, your character can be double annoying: first for having a higher bonus, and second, for casting guidance all the time (and demand others pander to your god for you to cast guidance on them).
[PS: Note that you may have to cast guidance in advance depending on how serious the DM is about this one-shot. I'd expect it to be rather lighthearted and would have fun praying for divine aid convincing the misguided right in front of them, given they asked you to create annoying characters. But if that does not work, you can cast it beforehand and keep it up for up to a minute, to avoid problems with casting a spell during social interactions. Or you can leave it out, in which case you will be back to the +7 to +9 base bonus you would have with a simple rogue build.]