Figuring out proper discipline for our own kids is a life-long process. Usually it's trial and error. When it comes to disciplining other people's kids, it's even trickier. Sure we don't want to tell our friends what to do, but we don't want to stop hanging around with certain friends because their kids are really annoying either.
I believe that learning to parent and discipline is a process that includes the helpful (and sometimes not helpful) advice of friends and family. And just as parenting advice in general from friends and family can be overwhelming and sometimes unwanted, I think that there are nuggets of good stuff in there that we can actually learn from.