I have never played in a casual golf game where all players played by the rules. I play with different groups during the week and here are my observations.
A mulligan off the first tee only if needed
A mulligan used any where if not used on the first tee
Rolling the ball anywhere
Rolling the ball if it lands in a divot
Moving a ball off of tree roots or rocks but not improving the ball position
Not putting out if the ball is inside the leather
Not putting out when playing as a team and your putt will not help the team score
Hitting a ball out of bounds and throwing a ball down in bounds in the area and taking a one stroke penalty
Loosing a ball and throwing down another ball in the general area and in the summer take a one stroke penalty or if it's winter take none as the "leaf rule" is invoked.
Picking up on a hole when you are having a golf meltdown
Loosing a ball, throw down another and strike it, then find original ball and play it with no penalty
Hit a ball out of bounds from the tee box and not re-tee another ball but go to the general area of where the tee ball went out of bounds and play from there with a one stroke penalty
Give advice to another player on what club to use
Hitting a ball in a water hazard and not taking the right line of where the ball entered the hazard in regard to the pin
The list goes on but I see the above situations play out every week. Does it bother me ? No. In my opinion there are two kinds of golf. Casual golf and tournament golf. The two mix like oil and water. Does anyone who plays this great game honestly play by the book every time they tee it up ?