I will be very surprised if anyone boos Kerry unless he smiles and waves at the crowd or attempts to open his mouth.
There is absolutely zero reason for him to intrude on the public. Neither senator from California is doing so, neither former governors is doing so, no Congressmen are doing this. So, it is an unnecessary photo op.
I don't expect boos, but I do expect a lot of muttering. And I hope he gets zero applause.