I haven't tested this much in Las Venturas. If you don't fancy spending a good hour chasing around miscreants and gunning them down, this is a cheap and easy way to rack up those levels and hit that coveted level 12 without breaking much of a sweat, or wasting your precious ammo. This only seems to work consistently with a few restaurants, and many of the ones in Los Santos don't appear to work at all. I'm unsure of why or how this works, but I believe it has something to do with how the game spawns enemies when you interact with interiors. For some reason, your targets are often destroyed as you leave the restaurant, or whilst you're wandering around inside. Walk around a little while (being mindful of you how long you have until the mission ends) and leave, getting back on your bike to replenish time. Simply start the vigilante, hop off your bike and enter the restaurant. I have had good results with the Cluckin Bell in downtown San Fierro as well. For best results, I use the Well Stacked Pizza in east San Fierro. This involves grabbing a police bike and finding a fast food restaurant.
There is actually a way to skip a massive portion of the vigilante missions.
