I've never seen a griefer, and I only play open mode. Must be because I do my thing away from Lave and the other systems where they watering-hole. Hint, hint, hint.
Indeed, I've only encountered 2 CMDRs in human space before, and both of my interactions with them were pleasant. One, we blinked lights and said "hi" and the other, he offered to shoot me up and I gave him a few tons of coffee not to. Good gameplay.
Human space is large enough that you can do anything you want without having to worry about griefers. Indeed, if everyone would just spread out a bit, it'd "grief" the griefers; they'd have to wait hours and hours for someone to come along and then you can just combat log or submit/boost or shrug and pay your insurance. Griefers get bored quickly.