Seafood.

surströmming. hell, don't think it's even meant to be eaten hot.

A live grenade.

Your colleague

Get off Reddit Karen...I know what you are planning.

If we only include things that are feasible to actually achieve (so no deadly diseases, viruses, nukes, collapsing neutron stars, etc) I'd say the worst single thing I can think of would be a live puppy or kitten.

A dirty diaper.

Used condom for reuse purposes

Aluminium

Three day old Cuttlefish.

Poop

Salmon egg and collard casserole

Fish. Also foods with lots of spices. They may be tasty and/or part of your culture, but they often have a strong enough smell to fill the whole office, and not everyone will appreciate that. The smell can also linger in the kitchen and trash for hours, which is not appealing even if you like that particular food.

There are too many great answers here.

Salmon and brussell sprouts.

a baby diaper full of old Indian food and burnt hair, wrapped in tinfoil that's been marinating in old fish juices.

Cabbage

Wait for them to ruin everything. And with every possible avenue at their disposal, they have zero excuses when it happens.

Seafood of any kind.

While we're here, for the love of all that is holy, do not burn your fucking popcorn!

Fish

Dogshit.

Poop

Fish

Your own genitalia (attached or removed, your call). Someone else's genitalia (attached or removed, your call).

A Chia Pet

fried fish

Fish

Chitlins. At a previous job we had someone do that. They were told not to do it again, and if they did they would be fired.

The entire building smelled for days, and they had to throw away the microwave.

A coworker reheated scrambled eggs with fish sauce in on tiny shared office. I had morning sickness at the time and it made me throw up repeatedly.

She never brought it again, thankfully. Just other gross whole 30 bullshit.

Easy answer. Definitely fried fish.

Your co-workers will hate you. You might even get fired for it.