I can't stand slamming doors, I'll normally go out of my way (running forward, waiting, etc) to avoid doors slamming in anyway. I tend to close internal house doors quietly by pulling the latch into the door (in which ever way the door handle/knob achieves that) close the door fully, then moving the latch back into the frame via the handle/knob.
The only exception to this I have is my front door, I won't slam it. I shut the door like above, lock it and rotate the key past the point where it moves the lock over (Its a barrel/skeleton key lock) and clicks, then rotate the key back to the point where it can be removed from the door without unlocking the door, then pull the handle down and push the door in so the door moves past the latch and catches on the deadbolt, it makes a kinda clicking noise when the deadbolt gets moved against the frame's bolt receptacle, then let go of the handle to release the latch then pull the door back towards me, if I don't hear the click of the latch going back into the door I will do it all over.
I really don't know what I'll do when I've moved house (Eep :< ) and my front door isn't a barrel lock anymore, most newer houses here are the tumbler style locks where the key won't rotate further than one rotation because they moved the bolt(s) into the door as you turn the key. I'll probably still try to open the door though.
I only really noticed this a few days ago when I skimmed over this topic and it made me think about it. It takes a good paragraph to explain but only takes about 4-5 seconds to do. I'm just a little paranoid about locking my front door I guess.
My car I always lock it twice, I've always had Vauxhalls (2 so far) and they have a double lock system, one turn of the key pulls the security tabs down and engages a bolt into the frame from the opposite side of the hinge, the second engages a thicker bolt on both sides of the door (I think)
End result is it makes two fairly loud clicks and electric motor noises, but I'd rather have the car locked than be quiet. Though I do walk quietly around my house, I try not to sneak up on people, I just walk quietly, Stompy people make me anxious, are they annoyed?