Ammosexual means: A person obsessed with owning guns; a zealous supporter of the right to bear arms.. It is informal slang, fine in casual speech but not suited to formal contexts. It is generally derogatory or offensive; worth a quiet word about how it lands on the person being described. If your teen uses it, context will usually make the intent clear. A short, curious question about where they heard it is usually all that is needed to know whether to follow up.