The crawfish po' boy is defined by how small and how many the protein is: a sandwich filled not with one fillet but with dozens of tiny fried crawfish tails, each its own crisp morsel, piled the length of an airy Louisiana French loaf and dressed. The mass of small bites is the point. Where a fish po' boy carries one large piece, this one carries a heap of individually coated tails, so every bite is a different ratio of crust, sweet crawfish, and bread, and the loaf has to be the airy New Orleans one or the whole thing fails.
The craft is in the fry and the dress. Crawfish tails are small, sweet, and quick to overcook, so they are coated thin, often in a seasoned cornmeal or corn-flour dredge, and dropped into hot oil for only a short pass: long enough to set a crisp shell, short enough that the tail stays tender rather than turning to rubber. They come out fast and go onto the bread fast, because a pile of tiny fried things sheds its crispness the moment it sits. The loaf is the thin, glass-crackly Louisiana French bread with a near-hollow crumb, chosen because it shatters cleanly and stays light enough to eat a foot of it, and crucially because it does not soak and crush a fragile fried filling. Dressed means the New Orleans system: shredded lettuce, tomato, pickle, and mayonnaise applied to add cool and acid against the rich fry without flooding the bread, sometimes with hot sauce or a remoulade worked in. A po' boy shop runs the fryer hot and the bread fresh, building these to order so the tails are still crackling when the loaf closes.
The variations follow the kitchen. The étouffée version abandons the fry entirely, spooning a thick crawfish stew into the same loaf for something between a sandwich and a plate; the remoulade dress and the hot-sauce build are standing local choices. These adjacent forms, like the wider po' boy family of shrimp, oyster, and roast beef debris, are their own sandwiches and deserve their own articles rather than being crowded in here.