The main things I remember about my grandparents are not physical abuses by any means -- that wasn't what they did -- but the subtle-like-a-brickbat comments:
1) You are so lucky we took you in and didn't let you go to foster care. If I mentioned that something the neighborhood kids were doing sounded fun.
2) You better behave / not do that; you don't want the social worker to find out. She'll send you back to John and Virginia! If I wanted to, for instance, go to a friend's daytime party with parents in attendance, or meet a school friend at the mall to wander around, window-shop, and split a treat.
3) We don't have time for that. If I wanted to, oh, participate in an extracurricular program or get free tutoring that might have meant me walking an extra three blocks from a different bus stop to get home 2 hours later a couple of times a week. (Keep in mind Grandma was a traditional housewife and the only things we normally did were church Sundays and Wednesdays and grocery shopping on Saturdays.)
4) Just like your mother! Any rebellion or boundary-testing, especially involving boys or just getting away from the house. I finally put a stop tot hat one. Aforementioned mother is the one who slapped me for telling her that my stepfather's tickling had gone too far and past the panty-line. I was 10.
So yeah, not horrible stuff -- just not letting me grow up and constantly reminding me how kid and generous they were. When I left at 18 I had no idea how to balance a checkbook or set a budget -- Grandpa had never discussed such things, though I did get to write out the checks for electric and such pretty regular so I'd know how much I was costing them. Since they were family and my court-appointed guardians, they didn't get the foster-care stipend, I guess. I know it was also rubbed in that they didn't get the social-security extra payment for me after Grandpa retired, as they "didn't want to put me through the hassle of changing my name" on school papers and such. (Dunno why, everyone knew me as the Null kid anyhow.)