Early fireworks at the Diddy sentencing hearing … federal prosecutors are slamming him as overconfident, and they say his respect for the rule of law is just “lip service.”

Prosecutor Christy Slavik is coming out swinging in the government’s opening statement … she’s insinuating Diddy’s expecting to walk free as early as today, claiming Diddy booked speaking engagements for next week in Miami.

Slavik says, “That is the height of hubris.”