Some Ideas

 The sentence we got gave our group a lot of options. When not to sleep. When not to propose. When not to accept a job offer. etc. Virtually every completion of this sentence brings with it hilarious scenarios. My group came up with quite a few, but in the end, we stuck with "when not to go outside".

 I divided the scenarios for "when not to go outside" into two categories. First for home and the second one for all other locations. Although I think we'll choose storylines based on the house. Creating multiple locations would eat up a lot more time.

when not go outside -> house

when there is an apocalypse

when you are on Mars 

when you are a vampire

when there is a volcano eruption

when you wear VR goggles

when you live in Australia

when it's spring and you have an allergy

when you are a sloth

when a murderous deer came to you after years to get even

when you're not in your own reality

when you are high

when you're sleepwalking

when the gravity is switched off

when you are a hologram

when there is a purge night

when you don't know how to

when there is an acid fosse around your house

when sun is a deadly laser

when you are a princess guarded by a dragon

when there is a giant bread slice outside


when not to go outside -> other locations

plane
spaceship - when you are on a spaceship and you don't want to die
ship
car
tube
submarine - when you are James Cameron seeking for inspirations in the abyss of Mariana Trench
seal centre
wardrobe