There’s a certain gifted dramatist who never cares to dine;
He abjures his soups, both thick and clear, his entrées and his wine:
Every evening at six-thirty, if a play he means to see,
He rings the bell and orders up high tea,
Though he knows how very deadly it must be.
  Pinero, you are a hero,
   For danger you care no pin:
  Albuminoids and tannin
   You tackle with a grin.
  You care not, though your digestion
   Such acts must surely mar;
  Oh! Pinero—ero—ero,
  You’re a hero, hero, hero,
   Yes, Pinero, yes you are.

Oh! Pinero, do be careful; my dismay I can’t conceal,
When I witness your devotion to that cataclysmal meal;
You’re the only man I know of who can write a play in style,
Most modern ones are absolutely vile,
So we shouldn’t like to lose you yet awhile.
  Pinero, you are a hero,
   But don’t be one any more:
  Your craving for eggs and muffins
   Your well-wishers must deplore.
  The stoutest of constitutions
   Curls up before high teas,
  So Pinero—ero—ero,
  Be a hero, hero, hero,
   On some other lines but these.

Notes:

DANGERS OF MEAT TEAS. When the tannin of tea is taken into the system, apart from albuminoid material, it is quickly converted during digestion into glucose and gallic acid, the former being a useful food substance and the latter less injurious than the original tannin. If, however, the tannin is taken in conjunction with albuminoid matter – as in the horrible meal dear to the hearts of a certain class of English folk called a “meat tea” – a leathery compound is very soon formed. In fact, says the “Family Doctor,” “meat teas,” or any other similar combination of albuminoids and tannin, mean dyspepsia. (Lancashire Evening Post, July 15, 1904)
Meat tea (also known as high tea) is the evening meal or dinner of the British working class, typically eaten between 5 pm and 7 pm. It typically consists of a hot dish such as fish and chips, shepherd’s pie, or macaroni cheese, followed by cakes and bread, butter and jam.

— John Dawson   

“Bedelia” seems to have been much on PGW’s mind during the summer of 1904, as this is the third reference in Vanity Fair alone. The popular American “Irish Coon Song Serenade” was written by Jean Schwartz and William Jerome, and published in 1903. You can see the sheet music and listen to an early performance at these links.
Arthur Wing Pinero (1855–1934) was a leading English playwright of both comedies and social-issue dramas.