Another gag gift
Gift-giving returns to the Fire Emblem universe in Fire Emblem Engage, which includes an array of food and flowers to dole out to party members in exchange for a bonding experience with tangible benefits. But if you really dislike someone, you can give them horse manure as a joke. Here’s where to find it, and how to give gifts.
Horse Manure can be acquired through several means
You can get a ton of Horse Manure for free (haha what a phrase) through the pet system in-game. As you complete missions, you’ll have the option to wander around small hubs, and speak to animals. Most animals you find there can be brought back to the stables in the Somniel hub (make sure you also “equip” them to the stables after you find them, by interacting with the barn door. Animals will then periodically find/drop items in there, including Horse Manure (which does not need to be from a horse).
Alternatively, you can buy Horse Manure from the Flea Market for 100 gold. The Flea Market is unlocked when you start Chapter 14.
Give it to anyone in the Somniel like you would any gift
To give a gift to an NPC, just walk up to them in the Somniel hub and select “gift.” Then select an actual gift, or the horse manure. Gifting Horse Manure will have the obvious side effect of providing no actionable bonus, and will typically trigger an emotionally charged response (like Panette saying “Are you trying to start a war?!”).
That’s really all there is to it!