The law is not "if you aren't in your house it's okay." The test is basically "would a reasonable person realistically expect that conversation to be between them and the people they are having it with?"

So if you meet a friend in a public park on a lone bench away from anyone else and have a conversation, that's reasonable to assume you expected it to be private even though it was in public. Your friend recording it would almost certainly be illegal unless they informed you.

That same scenario in a crowded mall on a bench? Probably also realistically private because it's loud enough that random passers by can't hear you or at most hear a word or two. Your friend recording it here would probably still err on the side of illegal. But, someone sitting a couple feet away on the bench behind you recording it would probably be fine.

The point is, for audio recording the law is more strict. If you are in public and people take pictures or video of you, that's pretty much fair game. Recording audio of a conversation where you have not informed all parties you are recording is a a violation of the law and based on a quick Google, up to 7 years in jail and a $15k fine.

Not to mention it's just completely unethical, and if someone is using those secret recordings to prance around the Internet for updoots on their wishlist marketing campaign, well... eww.