Slashers never pursue fat girls and rarely attack groups that include a fat girl. Fat girls, it seems, are Slasher repellent.
Having a fat guy in your group is also highly recommended. If fat girls are Slasher repellent, fat guys are Slasher fodder. It’s like that old joke: If we’re chased by a bear, I don’t need to outrun the bear, I only need to outrun you. Fat guys are, generally speaking, easy to outrun. They can also take a lot of damage, so they’ll keep the Slasher busy for a few precious moments while you seek a good hiding spot or, better yet, a weapon.
A few Slasher films in which the above advice was followed:
Behind the Mask: The Rise of Leslie Vernon