Of or pertaining to the cannabis plant, getting "blazed", "stoned", smoking some "tree" (hence the leaf origin).

The act of becoming leafed, or leafing, is becoming stoned, or blazing.

A person who rips leaves off evergreen bushes simply to tear them apart and throw away for the purpose of relaxation during a long journey on foot.

The finest pipe-weed in all of South Farthing

A feather.

The meme originated from a tweet where some girl apparently forgot the word "feather", so she called a feather a bird leaf.

The event in which a fart in your sleep leads to the gradual billowing of gaseous air up into your wife’s or girlfriend’s face throughout the night. Since this process is strikingly similar to the fermentation of cocoa beans under banana leaves in Central America, it is known as “Banana Leafing;” a close yet benevolent cousin to the malicious Dutch Oven.

Person who's sole purpose is to make their mess the problem of other people.

Derivation: Leaf blowers blow mess out of the property into streets and lawns of other people and don't remove the mess, but just relocate it.

Being called a "leaf monkey" or a "leaf monkea" is the greatest insult someone could possibly get.