If you choose to remain quiet while the PF is deviating from the safe flight path, you're simply not doing what you're supposed to be doing as the PM. The fact that the guy in the LHS is more experienced than you doesn't mean that they're infallible and can never screw up. And if they get offended by you notifying them of a deviation... Well, that sounds like a good candidate for the "CRM of the year" award. Any half-decent airline would steer clear of such a pilot.
That is not to say that some simple rules are not to be followed. First, stick to standard callouts as much as possible. Second, apportion your actions to the time criticality of the situation and to its impact on safety. Last but by no means least - remain professional and courteous. If you stick to those principles, chances are you will do just fine.