I've seen India fans do it (and much more) many times.
Australia fans slate their players and boo when losing.
West Indies fans can be hilariously fair-weather.
England, Pakistan and New Zealand seem to almost enjoy losing, especially England fans who sing louder when they're taking a beating.
I'd never boo my side, although I would have a shout at a player who was obviously uncommitted in the field.
If Pakistan don't perform well in any of their games, would you boo 'em?