An allergy sandwich is a peanut butter and strawberry jam sandwich. Lots of people have allergies to nuts and strawberries. The cool people, however, do not. They know the best pb&j is a pb with strawberry j.
Lulu: Oh man, what is that you're devouring?
Ramone: It's my allergy sandwich.
Ramone: You are mistaken. An allergy sandwich is the magical combination of peanut butter and strawberry.
Lulu: Oh, yeah, I'm allergic to strawberries.
Ramone: Loser.
When you're eating out a mexican from Tijuana and she let's loose a fart, which actually winds up being a shart and you ingest some of the sticky suprise, now that's a San Diego Shit Sandwich