You're driving the Love Fist limo only to find out that it's a armed with a bomb, and the only way to not set it off is to drive fast, a la Speed, until the group finally disarms it. Hilarity Ensues.
The fact that Tommy is constantly annoyed throughout the whole mission makes it even more funnier.
Jezz: Tommy pal, you gotta save the band!
Tommy: I'm getting bored of this.
Jezz: Which wire, Tommy?!
Tommy: The green one.
You drive like a lunatic all over town, running over innocents, gun down several people including cops, SWAT teams, FBI agents, and cause massive destruction of property, all in broad daylight and in plain view of every law enforcement officer in town. You are eventually arrested, and as you emerge from the police station (minus weapons and a small bribe/fine) you can hear Rosenburg in the background, "Tommy Vercetti is an innocent man!"
This exchange from the beginning of the mission "Supply and Demand":
Diaz (screaming at his VCR player): Eject! Plastic crap! You doing this to ME?! Who do you think you are, you piece of plastic SHIT!?! Aaaaargh! SCREW YOU!!! (Diaz shoots up his VCR, Tommy walks in)