So if the character was young and didn't know better and started off with - say KY Jelly - what difference would he notice if someone showed him the 'right stuff'? (and agreed with regular Astroglide - that stuff is banned from my home)

Night and day difference. Water-based goes sticky and awful really fast and doesn't even have a good 'feel' to it if that makes any sense.

It'll get you by in the beginning but once you use something better you look back and go "dear god, how did that _ever_ work..."

Major difference in heat transfer, doesn't break down with friction, big sensitivity difference. Silk versus burlap, seriously.

Also the small matter of if one is uncut.. having something like KY get all tacky-sticky IS NO FUN WHATSOEVER. You really want the TMI mental image? Untangling one's foreskin from around itself because the lube turned into glue = End of happyfuntiems.

Have at it.