Flog one's dolphin vulgar slang
A vulgar slang used to refer to male masturbation
To masturbate
Used to describe touching or caressing one's genitals.
The phrase starts with a verb, therefore, it needs to conjugate within the sentence.
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.