Everything that I've read about melons says that the best way to determine ripeness is to wait until the stem turns dry and brown. And also that when the stem dries it will 'pull away' sightly from the body of the melon.
Well the other day I was out pulling weeds. It was hot, and I was really, really sweaty. Well the heat must have affected my judgement. At one point I looked over and saw this Sugar Baby watermelon, and it just looked so refreshing and so...ripe. I checked the stem...nope, not dry. Not brown. Despite the voice of reason whispering in my ear, I plucked the thing up and whisked it into the kitchen.
I mean look at this thing, doesn't it just look ripe?
Well it wasn't.
Lesson learned. (I hope)