Our DS is 15 months, for the last few months bath times have generally been an extension of playtime where I try to get him clean and he tries to put as much of the water out of the bath as he can.
The last couple of baths have been a completely different experience; he has just sat there whimpering/semi-crying and not playing. The only other thing I noticed that he does prod his danglies whilst he is whimpering.
We have a couple of theories; one is that he might have an infection - I've read that bubble bath can cause irritations. But why would that be the case all of a sudden when he has had the same brand for a while would be another question.
The other theory is that he has just got to that age when he has decided that he would rather not be bathed and the danglies bit is a red herring because he is exploring his body more now. There are other ares where he is pushing his own independence.
I'd be interested to read others thoughts and experiences.