My favorites have already been posted by Angela! Especially when the newbie is bigger than me.
132. Um..., my head is over here. (after a shomenuchi that lands 6 to 10 inches to my right or left)
133. No, really, you're trying to control my hand. Try to keep me from moving. (during katatatori techniques).
134. Don't worry, we'll go really slow. I promise I won't hit you... this week.
135. I'm really glad you came tonight (use name or make sure I leanr their name!). I hope I'll see you again next class.