never reveal a secret or betray someone
as close as an oyster
to fight or argue frequently
Like cat and dog
completely different from each other
Like chalk and cheese
to compete unsuccessfully with someone
meet your match
to give away a secret
Spill the beans
in excellent state of health or physical condition
as fit as fiddle
to be the best
the cream of the crop
to be very calm/relaxed
Cool as cucumber
someone who is very similar in character to their father or mother
chip of the old block
to be very similar in appearance
be like 2 peas in a pod