The Watermelon Theory

I'm a little confused about a saying I heard the other day.  Maybe you guys can help me out.

RED SKY AT NIGHT, SHEPHERDS DELIGHT.

RED SKY IN THE MORNING, SHEPHERDS WARNING.

Don't get me wrong, I've heard this one before.  When Catherine and I were younger, our Mum was always trying to impart wisdom via some ridiculous rhyming sentence.  The Red Sky thing was one of her favourites.  That, and One More Tantrum And I Will Kick The Crap Out Of You.

...

Sometimes they didn't exactly rhyme.

Anyway, my problem is that I can't remember the meaning of the second line.  Shepherd's warning?  Warning against what?  I wouldn't normally ask, except that when I woke up at 5am this morning to pee, the sky was as red as a sunburnt bum on Christmas.  Something's coming, was my first thought.  Followed closely by my second, which read something along the lines of...Sunburnt bum on Christmas?  I need to stop drinking.

Speaking of Christmas, tell me what you want because I am writing my list.  I don't care how expensive it is, or how close we are - just tell me what you want and it's yours.  Provided it costs less than 50 bucks and I at least like you a little bit.  If you're not sure on that last part, a good way to judge is by answering this question:

Have I Ever Thrown A Watermelon At Your Head Before?

If you answered no, you can probably expect a Christmas present from me.

If you answered yes...I wouldn't hold your breath.

I call this The Watermelon Theory.  I plan on using the same system to cull extra guests from my wedding invitation list, seeings as it's basically foolproof.  The only person who lives in exception to the rule is my older sister Catherine.  I have thrown a watermelon at her head before, but she's also you know...my sister.  And as everyone knows, family trumps assault with an over-sized summer fruit.  Every time.