What does aggie mean in British slang?

"Aggie" is not a common British slang term. It's more likely you're thinking of "aggro", which is a slang term for aggression or hostility. It's often used in the context of confrontational situations or when someone is being aggressive.

For example:

* "He was giving me aggro all night."

* "There's been a lot of aggro in the neighborhood lately."

However, it's important to note that "aggro" can be used in a less serious way too, sometimes to just mean someone is being a bit rude or pushy.

It's also worth mentioning that "aggie" *could* be a shortened form of "agriculture" in some specific contexts, but that's not slang and is much less common.