[Feature] Add more snark

[ducoterra]

Is your feature request related to a problem? Please describe.
We really need more backtalk from the bot. When someone declines, they should feel judged. When someone accepts, they should feel like a nerd. Let's make it happen.

Describe the solution you'd like
/rsvp accept
"Why even bother acceptings? We both know you have nothing better to do."

/rsvp decline
"Your party wishes you'd throw acid on yourself."

Describe alternatives you've considered
Being nice just doesn't cut it.