I've seen "THAT dad" so many times its made me wonder if I was once him? I hope not. 
Looking at HS->college players isn't that hard for me anymore. I'd say it may have once been, but its pretty obvious now. There are 2 kids at my daughters HS - one headed to Vanderbilt next year and the other headed to South Carolina in 2 years. I didn't know the second one at all - but went to a game just to see how good these kids were. They play on a pretty darned good HS team in the Raleigh area so they are surrounded by good HS players.
It was SOOOOOO obvious before the 1st innings was over - both on the field and at bat. I could pick out the 2nd player (whom I did not know) easily. Their movements are so different than everyone else's - its kind of like looking at LL tryouts where the top couple of kids stand out head and shoulders above everyone else.
But still...I am certain that other parents on that team see their own sons at close to the same level as the two players that are moving on to high level D1. Nothing bad about those parents - none of them were behaving like 'THAT dad' but I've been around parents enough...and been one long enough myself...to know its just too darn hard to fairly evaluate your own kid.