Definition
A generic, cheerful greeting said to someone in the morning.
Origins
A working-class phrase once popular throughout the British Isles, possibly in reference to cream rising in milk. It has been revived into popular consciousness, and is associated with Irishmen, by the film Darby O'Gill and the Little People (1959).
See Also
How People Actually Use It
It's jacksepticeye 's intro. After loud *WWHHIIIPPSSSHHH* (slapping sound) he High-five the air and scream these words: "TOP OF THE MORNING TO YA LADDIE, MY NAME IS JACKSEPTICEYE, AND WELCOME BACK TOOO...(the name of the game he actually play) (...)"
"-in jacksepticeye 's intro, also very often used by his friends (especially pewdiepie) and his fans and all of bosses -instead of "Hi" or "Good morning" you can just yell "TOP OF THE MORNING" -ATTENTION: you should scream these words, because it's correct and required way to say it"
Source: Urban Dictionary