If someone randomly approached you and was trying to show or express genuine romantic interest, would you react positively or react defensively?

I've never had someone randomly approach me and show anything that I could pick up as being genuine romantic interest, so I can't really say with any level of experience how I might react.

I suspect though seeing I'm very introverted and have bad social/sexual phobia that I might react defensively and brush off the approach as a bad joke even if it was actually legit and not trying to have a lend of me.

I'm terrible with body language, etc and don't understand 'choosing signals' or love languages or whatever you want to call it when a person has confidence enough to approach and/or flirt with romantic and possibly sexual intent. I definitely can't flirt for the life of me.