could just be that he is a baby who cries a lot...my son did....never seemed to stop unless out and about...but with others he was fine..opposite to your problem really. I assume you have asked mum what the is like at home and how she deals with it when or if it happens. A consistent approach by all may help a bit.

must admit to leaving him for a while to get on with it, but that was my own child....he was always worst when waking up...such a temper...even now he still hates waking or being woken up...avoid at all costs for at least an hour !! (22 now!)