Boat Casual
A dressed-down preppy who is still wearing fancy clothes.  Like if they were going out in their boat, and were scared that the surf would be rough and get them all wet, so they wore Topsiders, khaki shorts, and a t-shirt from a 10K race from eight years ago.
Definitely a WASPy Dad look.
His Dad was kickin' it boat casual on the back deck by the grill, getting barbecue sauce on that old pair of Dockers shorts that he wears whenever he does yardwork.