It’s not illegal to take pictures of people in public. I get that it’s creepy, but where does one draw the line?

Most countries have mastered this nearly impossible task of drawing the line quite well.

In many everyday situations, yes - it may be legal to take a photo of someone in public.

Australia doesn’t have one single “photography law” that bans taking photos of people in public. Instead, the legal risk tends to come from a mix of areas, like:

• privacy and surveillance laws (which can vary significantly by state/territory, and can apply even when you’re not “hiding” what you’re doing)
• consent and image releases (particularly for commercial/promotional use)
• workplace surveillance rules (if staff are involved)
• australian consumer law risks (for example, misleading or deceptive conduct if an image implies endorsement)
• defamation and reputational harm
• harassment and related conduct
• where the photo was taken (public place vs private property)

(source)

It's very similar in my home countries.