G. is addicted to greasy food (cholesterol) i.e. lasagna.
Since G. is on a diet, he thinks that he's suffering from symptoms of (cholesterol) withdrawal (cold turkey - if that doesn't make it even worse for you) that an alcohol addict would be likely to suffer.
G. is daydreaming (having the urge) of having a bacon grease cocktail (pure cholesterol) just like an alcoholic would have an urge to have a drink.
Definition from a dictionary:
highball
# A cocktail served in a tall glass and consisting of liquor, such as whiskey, mixed with water or a carbonated beverage.
Okay?
Ask away...
I've got it completely, thank you so much!