Basically, I think Prudie misread the message and misanswered the question.

The issue here is that most people are very short-sighted and have a hard time understanding that what they enjoy, which is what they think other people would enjoy, is not actually enjoyed by everyone. Thus, this guy, who probably enjoys laughing and physical contact of a playful nature, is having a hard time seeing past his own mirrored glasses. He is not successfully seeing his girlfriend and her needs/wants/desires despite her communication of them. He does need a moment of clarity and a chance to mature and see her better. He will probably still find this whole situation counter-intuitive. He may continue to tend to think that she will enjoy tickling. He will need to be mindful to remember that she doesn't. However, this can take a little time and a little doing, to bring him to this understanding. Simply deciding he is a sadist doesn't really help anyone.