When she is doing it just say ouch babe not too hard.
is part of a discussion in the Sexual Foreplay and Techniques forum that includes topics on Need to learn that special place to put your tongue or do you just want to spice things up?.
I like being told what to do less or more of but thats really a personal thing some females may feel hurt by this the thumb idea could work or simpley being up front and honest may work also its all to do with the wording of it always start with a complement just so she doesnt feel put down and like others said you dont want her to stop doing it all together
Don't talk to her about it during a time of intimacy. Talk about it later, when you're not being intimate. She's more likely to be offended/have her feelings hurt if you talk to her about it during a time of intimacy.
I would definitely want my husband to tell me if I could do something better to heighten his enjoyment, even if that means telling me I'm doing something wrong.
