Similar to Bob’s Your Uncle, Jean-Guy is a common french name.
Jeweller’s Hammer
Any especially large or heavy hammer or mallet-like implement. [Non-AvE word, but is an AvE joke since a real jeweller’s hammer is a very small, delicate hammer. Canadian spelling, as AvE is Canadian.]
Jelly Bean[er]
Any IC or simple active electronic component now so commonplace that its price is negligible and its brand is largely irrelevant. [Non-Ave Word.]
Jeezless
Spiritless. [Unknown. Reminiscent of “Jesus, but usage is totally different. “If I can fix the Jeezless thing.]
Jazz Hands
To type. “I did the ol’ jazz hands routine on the gargler and found this.
Infernal Combustion Engine
Internal Combustion Engine
Japscrap
What your daddy named his low-grade tools & material before China got into the game.
HPHT
Hot Pink Hockey Tape. Reference to High-Pressure/High-Temperature.
Hot supper
1. Working it very hard, 0%. Commonly as “given her the hot supper.
Hot dog down a hallway
1. A loose fitIronically, a perfect fit. (Source)