As Rajun says, there are decent players out there but, because we're not in your face shooting you all the time, it feels as though Los Santos is nothing but idiots. I try to play the game as I would imagine I would in real life if I was really into heavy crime such as grand theft, armed robbery and assignation. I would never approach you unless you were where I wanted to go amd then I would do so quietly but carefully and will only shoot if shot at. If I join your mission, I assist to the fullest but I would always wait for your arrival before opening fire as it's your mission. I would ensure you pickup the vehicle/coke/evidence whatever the mission is, and cover your back while you deliver. Once the mission is over, I then quickly disappear into the night and will sometimes leave a text 'good work' if I felt that was the case. This to me is the real way pro criminals would work...quickly, quietly and proffessionally.
Then there's the scally type crooks...shoot their own mother, rob their own kids...blow up anything, shoot innocence along the mission to ensure a healthy supply of cops...operate without a suppressor, honk their clown horn, crash everything in their rush to beat you to your mission, rush to do everything in your mission before you, dying multiple times in the process ensuring that if you die, you have to spectate. Then shoot you after mission and crash everything on their escape with a flood of cops and choppers at their tail. These people also think they're 'awesome' at the game lol