Trigger is just bob.
However, you may want to prompt for for the checkered red overalls or something to break out of the style.
This lora tends to give a retro effect and FLUX will lean towards glossy fiberglass characters (as this is trained on a large glossy fiberglass statue from the 1950's).

I threw this together as the recently departed David Lynch used to frequent a Bob's Big Boy restaurant in Burbank. I found myself wanting to generate images of this Bob, but FLUX wasn't doing it.

It works well with regular old FLUX, but it seems to work even better for Acorn Is Spinning FLUX. I also generated some images with both and the one's with the acorn in the photo are there to make the Acorn Is Spinning FLUX generated images easier to spot.

So who the heck is this Big Boy mascot?

From wikipedia:

The chain is best known for its trademark chubby boy with a pompadour hairstyle wearing red-and-white checkered overalls holding a Big Boy sandwich (double-decker cheeseburger). The inspiration for Big Boy's name, as well as the model for its mascot, was Richard Woodruff of Glendale, California. When he was six years old, Woodruff walked into the diner Bob's Pantry as Bob Wian was attempting to name his new hamburger. Wian said, "Hello, Big Boy" to Woodruff, and the name stuck. Warner Bros. animation artist Ben Washam sketched Richard's caricature, which became the character seen on the company trademark. In 1955, Bob Wian hired Manfred Bernhard, son of graphic designer Lucian Bernhard, to create a new public image for Big Boy. Bernhard was not impressed with Washam's mascot, saying it was sloppy and had a moronic expression. The "West Coast Big Boy" mascot was revised, fiberglass statues molded, schemes created for menus and building designs, and a comic book for children launched.

(Big Boy logo used from 1988 to 2020, featuring the Big Boy mascot and still seen at many locations)