I kid myself that I always pick up on things like this, but I don't. If I ever do it's, only about a day later at best. My neighbor is moving house and recently separated from her husband. Some time ago she brought wine and chocolate around to my house, to thank me for putting her waste bin out, when she was on holiday.
I guessed something was odd, she was trying to chat, it seemed over generous, but I'm a simpleton and I just accepted them awkwardly, kept the conversation as short as possible, then closed the door. My ex had been gone for months and I'm sure my neighbor must have known that. I could flatter myself but I'm equally sure, if she was hitting on me, it was only due to her being lonely. We've barely had a conversation prior to that, whilst she'd often talked to my ex.
If I'm hitting on anyone, I'll always try a little Shakespeare or poetry out on them. That way when I crash and burn, I feel better about it. Also I usually either blush, stammer, knock something over, or accidentally break something. Maybe all at once, depending on whether I'm just anxious, very anxious, or hyper ventilating anxious. On the very few occasions I stay calm, and avoid those issues I usually blow it some other way. Standing on their foot, criticizing that nasty guy (who turns out to be their best friend or relative) or similar.
Apart from that I enjoy flirting...It's a hoot..