Brimming with energy, boisterous, assertive, full of beans.
To say that people are “full of piss and vinegar” is to say that they are brimming with energy and enthusiasm. In the distant past, similar phrases had a rather negative connotation, but the modern expression is usually complimentary, “vinegar” being an old slang term for enthusiastic energy.
Here are the more negative sources:
In 1602: in Return from Parnassas — “They are pestilent fellowes, they speake nothing but bodkins, and pisse vinegar.”
In 1922: In Ulysses, Joyce writes — “All wind and piss like a tanyard cat.”
‘Wind and piss’ is usually taken to mean empty talk, full of bombast. Vinegar is associated with sourness and acidity in many other citations.
The earliest written form of the phrase appears to be in John Steinbeck’s 1936 novel, In Dubious Battle:
“Listen, mister,” London said, “them guys is so full of piss and vinegar they’ll skin you if you show that slick suit outside.”
Steinbeck must have liked the phrased because he repeated it in The Grapes of Wrath in 1938.
The word “vinegar” has been in the language since the 12th century. Early in the 20th century, it was used to mean vitality and energy and meant much the same as “vim and vigor,” which is also still in use today. The phrases are similar but “vim and vigor” usually implies an innocent youthful energy, whereas “piss and vinegar” suggests a more mischievous vitality.
The phrase, “full of beans,” goes back to 1854. Another expression, “to piss vinegar,” goes back to 1602, and means ‘to be miserly.’ This gave rise to the 18th-century “vinegar-pisser,” a ‘miser.’ So, the next time you go to lunch with someone who doesn’t want to share the bill, you’ll know exactly what to say!
Some people try to make the expression more polite by substituting “pith” for “piss,” but this change robs it of the imagery of acrid, energetically boiling fluids (have you ever seen a horse let loose?) and conjures up instead a sodden, vinegar-soaked mass of pith.
It’s fun to use as it stands, a satisfying and descriptive way to express either enthusiasm or frustration with someone’s antics.