In Lily's defence, Perez kind of deserved it: after calling Lily an "awkward cow" on his blog, Perez took to Twitter and asked for a role in Lily's latest video clip, currently shooting in LA.
(If you're not cool enough to know what Twitter is: it's a blogging tool that limits each post to 140 characters. Lots of celebrities have one. It's neat.)
"Oh , I'm sorry , we've already cast the jealous and bitter lonely old queen role," Lily fired back via her own Twitter account. "Next time, eh?"
From there, it descended into a gloriously nasty back-and-forth that culminated with Lily blocking Perez so she wouldn't have to put up with him anymore. Read the whole sorry mess here:
Perez isn't the first celebrity who Lily has tangled with. Relive some of her greatest, meanest insults in our gallery showcasing her many high-profile feuds.
We're firmly in Team Lily in this particular battle... who do you support?