Donald Trump thought he landed a nice jab at Hillary Clinton by basking in her decision not to run in 2020 -- but looks like she's getting the last laugh.Trump took the first shot Tuesday, tweeting -- naturally -- his response to "Crooked" Hillary not running ... "'Aw-shucks, does that mean I won’t get to run against her again? She will be sorely missed!"Hillary did promise to continue fighting for what she believes in ... and looks like giving Trump the business is on that list. After his Twitter-diss she clapped back "Mean Girls" style.She posted a classic GIF of Rachel McAdams' character asking Janis why she's so obsessed with her.Hard to argue with that -- years after his 2016 victory, POTUS never passes up an opportunity to reference her and never glowingly too.