REWARDS - Respect, Dancing unlocks
This mission can only be triggered between 22:00 and 6:00 on the in-game clock.
Head to Verona Beach to find the beach party. When you get to the party, talk to the DJ and reply positively. You need to dance a bit to impress the DJ enough to gain access to the van. This challenge is similar to the one with the lowrider where you had to time button presses in the circle at the bottom of the screen. You need a score of 4000 at least to gain access, so pay attention to the buttons at the bottom of the screen.
Once you get a score of 4000, follow the DJ into the sound van and then hijack it. Once you get in the van, step on the gas and get away. The DJ will fall out and the people at the party will start firing. A car will chase you as you drive to the yellow blip on the radar. The mission ends when you drive into the red marker at the garage. You earn some more respect.