Ooh! Great question! I love idioms!
Don't be wise after the event! <- this is not a phrase
Don't make a fuss after the event! <- also no, sorry
Don't fuss around after the event! <- nope, sorry!
Don't beat a dead horse! <- stop talking about it! Although usually we use it when we want to apologise for continuing to talk about something. Especially in Britain. "I don't mean to beat a dead horse, but I still don't understand what happened, could you explain it again?"
- Thanks for the history lessons! <- Ooh I love this phrase! It's very rude though. Probably said by a teenager or someone who is passive aggressive. If my brother is telling me all the mistakes I've made I might snap and say "Thanks for the history lesson!" but what I mean is "SHUT UP!"
- That's old news! <- I already knew this.
Friend 1: Did you hear that Jack broke up with Clara?
Friend 2: That's old news! They posted it on Facebook three days ago! But have you heard who Clara is going to ask out?
I hope this helps, I completely agree with what Summer's said and it's always good to get more examples!