1) act as a guinea pig
— to allow some kind of test to be performed on someone
I was not happy to act as a guinea pig for the new training material.
2) as awkward as a cow on roller skates
— very awkward
The little girl was as awkward as a cow on roller skates when she first began riding her bicycle.
3) as clean as a hound's tooth
— very clean
The classroom was as clean as a hound's tooth when the students finished cleaning it.
4) as conceited as a barber's cat
— very conceited, vain
My friend became as conceited as a barber's cat after she won the award at school.
5) as crooked as a dog's hind leg
The politician is as crooked as a dog's hind leg and nobody trusts him.
6) as drunk as a skunk
— very drunk
The man was as drunk as a skunk when he walked into the restaurant.
7) as hungry as a bear
— very hungry
I was as hungry as a bear when I arrived home from work.
8) as innocent as a lamb
— having no guilt, naive
The little girl is as innocent as a lamb and everybody loves her.
9) as poor as a church mouse
— very poor
My cousin is as poor as a church mouse and never has any money to spend.
10) as scared as a rabbit
— very scared
I was as scared as a rabbit when I entered the empty room.
11) as sly as a fox
— smart and clever
The manager of our apartment is as sly as a fox.
12) as strong as a horse/ox
— very strong
The man was as strong as an ox and easily helped us move the sofa.
13) as stubborn as a mule
— very stubborn
My friend is as stubborn as a mule and you can never make her change her mind.
14) as weak as a kitten
— weak, sickly
The girl is as weak as a kitten and cannot carry the books.