I'd be up for a no phones, tablets or other noisy devices cafe. I find it so sad when these are used as calming techniques, children miss out on so much with their eyes fixed on a screen. It's also annoying to hear lots of loud half conversations, or the volume of multiple short video clips being watched.
At different times I'd also be keen on a no dogs cafe.
Children-wise, generally I like children that are either well-parented or well-behaved, but agree if the child is screaming then take them out or try at least to calm them.
I'd also put a ban on those loud people who are always bragging about how wonderful they think they are, except they just seem rather annoying.
Also, giggly groups of students.
Also smelly people, good or bad, some people just smell really strongly.
Maybe I should just have a cup of tea at home...