Stepfather parenting

My daughter remarried 3 years ago and already had a 13 & a 15 year old.  He is a nice guy but, in his words, "his stepson drives him crazy". Granted, my grandchildren were lacking in manners and respect, but he feels it is now "his job" to teach them manners.  He calls my grandson on things he perceives as "bad manners" at the table, in public, to the point where I am embarrassed and feel bad for my grandson. In my opinion, he should be modeling good manners and patience with his teen stepchildren.  He disagrees; "I'm the dad and it's my job and I'm just giving them a taste of what the real world is like". I know my grandson really resents him and will fly as soon as he is able.  He has threatened to "go live with his dad", but believe me, that would be worse for him.  Anyway, I tried to talk with my son-in-law, but he just disagreed and walked out.  So much for experience!  What should he be doing?
ps/there is his son age 6+ and, together they have a 3 year old and a 1 year old in the home

[Kevin Kennedy, Ph.D.]

The boy's behavior was not at all unusual and was not an example of poor manners. Developing reasonable expecttaions of our children is an important part of parenting, and in this instance there was really no reason to reprimand or 'teach' the child anything.

[Kevin Kennedy, Ph.D.]

To his credit he is trying to act like the parent instead of abdicating his responsibility, as some stepparents do. Now, is he doing it in the best way, or even a reasonable way? That I don't know from your description. Hopefully he can adopt a constructive approach to criticism. It sounds like the grandchildren need some limits and some learning that they did not receive earlier in their lives.

[pt49er]

I guess my question is, what would be the best way, or a reasonable way to "teach manners" to a 16 yr old by a stepfather?  I will tell you the latest incident; we were all at the Senior Banquet for his older sister. It was buffet style and the beverages were just out the door on the patio.  Stepfather stands up and asks where the drinks are, I said outside (he said later he didn't hear me), he asks 16 yr s-son and he points in the direction, asks again, points again. (the building was small and if you could see around the corner you could see the drinks, AND, we were the table next to the door!) Stepfather takes his pointing literal and turns around and walks into the wall!  He counsels s-son that he should have said "out the door, to the left" (manners). I was embarrassed by this public display, and I'm assuming my grandson was too; after all, it was not only in public, but it was at a school function with other families and high school kids,  Good grief!  THAT is, apparently, what he calls "teaching manners"!