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
If a person has the devil's own luck, he or she has extremely good luck.
A: Yesterday I won a $10 million lottery jackpot and today I won a car in a draw.
B: You have the devil's own luck.