The EU was specifically meant to prevent countries taking actions in their own interest, to stop them from putting their own interests above those of other countries. Now that is done and France can act in France's interests, which probably aren't exactly the same as Britain's. They are now free to make the rational decision to, for example, place tariffs on British goods so as to protect French manufacturers.
Great for European unity, I see.
The UK never believed in the EU and only wanted the good side of it. It's better for everyone that they'll be gone. There was no European Union if a selfish state didn't want to be united in the bad things too.
If the EU as a whole decides for a new trade agreement with the UK, that's fine (See? Unity), but I think they won't since the EU has strong motivation to slap back the UK.
French know this will happen, so they don't do that.
Wait until Berlin replaces London as an economic hub.
Economic war will ensue and we'll all lose.
When negotiating, you never let a position of power go to waste.
Why? Out of pique? Out of being disrespected? Out of a general tit for tat?
I don't agree with the UK voters today (from my safe spot of not being a UK voter) but it seems pretty silly for the EU or countries within the EU to treat this vote--assuming it goes ahead--as a petulant child would, damn the consequences. They should and probably will make a rational response based on their own interests whether or not they're "annoyed" or whatever the word is with the UK.