hat tip noun (informal)

An acknowledgement of respect

hat trick noun

1. A conjurer's trick with a hat
2. (in cricket) the taking of three wickets with consecutive balls (orig considered as deserving a new hat)
3. A corresponding feat (such as three goals scored by the same player) in other games
4. Three successes in any activity

a bad hat (informal)

A rascal, an unscrupulous person

hang up one's hat see hang

hats off to

(give) all honour to

horse and hattock

To horse (traditionally a signal of witches or fairies)

mad as a hatter

Completely mad (poss from the odd behaviour of some hatters due to mental and physical disorders caused by the mercury in the chemicals used in the making of felt hats)

my hat!

An exclamation of surprise or disbelief

pass or send round the hat

To take up a collection, solicit contributions

take off one's hat to

1. To acknowledge in admiration (figurative)
2. To praise

talk through one's hat

To talk wildly or nonsensically

throw one's hat into the ring see under ring¹

under one's hat

In confidence

wear several hats, another hat, etc

To act in several capacities, another capacity, etc