Obligatory trivia about word origin’s (you know I’m into that):
You will notice the sign on the counter advertising the “gedunk sundae” which became so famous that the cartoonist had to invent a recipe for it.
It’s likely that the word gedunk originated in this strip, but it later became popular slang in the U.S. Navy, referring to an ice-cream soda, sweets in general, or even snacks in general. Examples of this word date back to at least 1927. From there, it developed into a name for an ice-cream stand and later a snack bar or canteen store, usuallyon a ship of the U.S. Navy or Marine Corps. Examples date back to 1956 and it was still current until at least the late 1980s, according to the Random House Historical Dictionary of American Slang, published in 1994.
There are various stories about the invention of the sundae, but it seems that it began as an ice-cream soda without the soda. Sodas used to be made with ice cream, chocolate or other syrup, and pain soda water. There was a place that forbid the serving of soda water on Sundays (prohibition and all that) and one story goes that shops got around the law by serving ice-cream sodas without the soda water on Sundays, and thus the sundae was born.
Here’s a good summary of information about the Harold Teen strip: http://www.toonopedia.com/teen.htm