As Sick as a Dog

Last week I had the worst case of strep throat I have ever had in my life, which is saying a lot since I used to get strep at least once a year up until 12 years ago (the last time I had it).  The thought popped into my head that I was sick as a dog (might have been when my fever reached 103 degrees and I was projectile vomiting in five different directions), but in any case, I wondered why we say sick as a "dog".  I have a dog and have seen her sick, but not any worse than I have seen Bob in our younger partying days after a night of too many 7 & 7s!! So, I found a British web site that lists sayings in alphabetical order (see what happens when I am sick- way too much time on my hands!).  Some were very familiar, others not so much, but they made me laugh! So, I have listed the not so familiar for your reading enjoyment!
As Irish as Paddy's pig
As bald as a coot
As black as Newgate's knocker
As black as the Earl of Hell's waistcoat
As boring as a wet weekend in Wigan
As boring as watching paint dry
As busy as a beaver
As busy as a one armed paper hanger
As busy as a one legged arse kicker
As cold as a well digger's arse
As common as muck
As crooked as a dog's hind leg
As cute as a bug's ear     how cute are bugs, let alone their ears?????
As dead as a dodo
As different as chalk and cheese
As difficult as nailing jelly to a tree
As drunk as a lord
As dry as a pommy's bath towel
As fine as frog's hair
As fit as a butcher's dog
As full as a fat lady's sock
As full as an Alabama tick
As happy as a dog with two tails
As happy as a sandboy    ??????
As happy as Larry   Not sure who Larry is and why he is so happy
As keen as mustard
As mad as a bear with a sore head
As many chins as a Chinese phone book
As near as dammit
As pissed as a newt
As queer as a chocolate orange
As queer as a nine bob note
As rare as rocking horse shit
As sure as eggs is eggs
As tight as Dick's hatband
As tight as a duck's arse
As useless as a chocolate fireguard
As useless as a chocolate teapot
As useless as tits on a boar
As weak as gnat's piss
Leave it to the Brits to come up with some good ones!!! To a Brit, being sick means one is vomiting; no vomit, you are simply ill, not sick.  So, when you are sick as a dog, it is refering to a dog vomiting, which after further consideration, I guess is pretty darn gross at times.