A little long in the tooth

This means you are getting old.

This is based on horse teeth keep growing and if left unattended, can get very long.  Other animals' teeth keep growing as well, mostly rodents.

Built like a Brick Outhouse

Traditionally, outhouses or shit-houses where made of wood due to the fact that they had to be moved fairly regularly because the holes kept filling up.

Brick outhouses where usually only done by the wealthy and very fancy.

Of course, brick outhouses are much stronger than their wooden counter parts.

Hair of the dog

The root of this is "the hair of the dog that bit you".

This literally refers to the misguided belief that if you were bit by a rabid dog, you need to pluck a few hairs from it and put it on the bite wound to prevent getting rabies.

Oddly enough, around the time of William Shakespeare, many European countries had almost identical sayings that related to both rabies and hangovers.

(usually talking about drinking but still makes no sense  :P)

Smart Ass

The root of this phrase is "smart Alec" and is based on the exploits of Alec Hoag, a celebrated pimp, thief, and confidence man operating in New York City in the 1840s, Hoag, along with his wife Melinda and an accomplice known as "French Jack", operated a con called the "panel game", a method by which prostitutes and their pimps robbed customers.

Military Intelligence

At best, this can only be classed as an oxymoron and not a saying, so I can't give a basis for it.

Military Intelligence(please take no offence)

Bite the bullet

You often see in period dramas that they have women bite on wooden spoons while giving birth.  Well, it's claimed that in war time they had soldiers bite on a bullet to take their mind away from the pain of their surgery; ie amputating a limb.

Kick the bucket

When someone would commit suicide by hanging, they often used a bucket which they would kick to hang them self.

Face the music

The expression “face the music” comes from the military “drumming out” ceremony for disgraced soldiers.  This ritual called for only drums to accompany the dishonored as he was stripped of his rank and colors in front of his assembled unit.  For cavalrymen, this humiliation was enhanced by having the offender sit backwards on his horse so that while leaving he could still see, as well as hear, the drums and the band.

Drunker than a skunk

This appears to be a fairly modern phrase.  Despite what you see in the movies, it seems that the earliest use of the phrase didn't start until the 20th century.

The best that anyone can guess, it seems to be based on the fact that it rhymes and that skunks and drunks stink.

Caught red handed

This is being caught with the blood of your victim on your hands.

Got up on the wrong side of the bed

This is a Roman superstition.  It's bad luck to to get out of bed on the left side.  Doing so will make you grumpy all day long.

If you notice, day beds are made so you can't get out on the left due to it having a back on that side.  You can only get out on the right side.

Under the weather

It was believed that weather can make you sick, so you were under the influence of the weather or more commonly "under the weather".

Kick the bucket

Face the music

Drunker than a skunk

Caught red handed

Got up on the wrong side of the bed

Under the weather**

Dead as a doornail

This is based on 2 things.  Doors were often used to carry the dead and when they got to the funeral parlor, they dismantled the door and used the nails for the coffin.

Fit as a fiddle

A violin was considered extremely delicate, while a fiddle {technically both are the same instrument} is considered robust.

As poor as dirt

Poor people used to have dirt floors

As right as rain

It's meaning is similar to "fit as a fiddle".  During the 19th century and on into the 1930s, there were many droughts and rain fixed the problems and made the crops grow. So rain made everything "right".

Sick as a dog

Dogs tend to be energetic, but when they get sick they really get sick and lethargic.

Brits tend to use "sick as a cat".

It's raining cats and dogs

There are several theories for this one.  The most gruesome is that in bygone eras, drainage was so poor that stray animals, usually cats and dogs, would get drown in hard rains.  When the rains were over, people would see all the dead cats and dogs and think they came with the rain.

Colder than a witch's tit

Supposedly, this is from the witch hunting days of old.  People believed that witches had no maternal nature and therefore a baby couldn't suckle from her tit.

Another one that's never made much sense.  Did a dog chase a cat up a tree during a rainstorm and they both fell off the branch while someone was passing by, so the person yelled "it's raining cats and dogs?

Colder than a witch's tit

I've never touched a breast in my adult life, so this one might have merit  :rotfl:

Fit as a fiddle

As poor as dirt

As right as rain

As Sick as a dog

A stitch in time saves nine

This refers to needle point.  Supposedly on average, you have to undo 9 stitches to repair a mistake.  So if you see your mistake right away, you were saved from having to redo 9 other stitches as well.

Sleeping like a baby

During the Victorian era, many baby "sleep aids" contained opiates, so babies sleep very quietly.

Clean as a whistle

Refers to cleaning ship and train whistles during the steam engine's reign.

Cute as a button

This refers back to the days when only the wealthy had buttons on their clothes.  And of course, the clothes of the wealthy were considered the height of fashion.

I was beside myself in disbelief

The Greeks believed that the body and soul were 2 separate being that made up humans. Under great emotional stress, the 2 could separate.

A bird in the hand is worth two in the bush

This is a hunting based saying.  Having 1 bird already caught is worth more than twice as many uncaught.

A stitch in time saves nine

What the hell's a stitch in time?  And what does it save nine of?  ???