30 second Egg Poacher
Boiled egg breakfast in 30 seconds!
Crack an egg into this, microwave for 25-40 seconds (soft or hard boiled) and eat!
PET or PETG is probably a good choice of filament to use. PLA goes soft with heating and ABS can contaminate the food with harmful chemicals. Other materials are also suitable but do your own research.
The print layers can make this difficult to clean and bacteria will develop. You should wash thoroughly before and after use. You could also consider post print processing such as applying a coat of polyurethane.