For (a/some) reason(s) best known to (oneself) humorous phrase
When describing someone's behavior, this phrase is used to imply that it is perplexing or perverse.
Justin, for reasons best known to himself, was putting chopsticks on his ear.
For reasons best known to herself, Jane refuses to receive the full scholarship of Harvard university.
Although nobody is here, Bin keeps whispering in my ear for reasons best known to himself.
Used to ask whether the word "funny" is being used to mean "humorous" or "strange"
If there's a rumor about someone or something, there must be a good reason for it.
A crazy, strange, or eccentric person
Used to allude that the last force, problem or burden which is seemingly minor and small causes a person, system or organisation to collapse or fail
Her husband's violent act last night was the straw that broke the donkey's back and she left him