Sonic smile

Say one is cuter than the other, than say nevermind, the other one is

Hmm any better ones

Tell them women don’t really exist and are just a figment of horny males’ imaginations

Hmm any better ones

Claim that one of them told you that they actually hate the other one so much they would shoot them rather than the greatest villains in history.

walk up to them and say this: "A centar has six limbs, and is therefore an insect. discuss."

what

they'll argue if it is an insect or if it isn't

but that’s only an argument
I want drama
Like actual twitter drama

but then their arguing will cost their friendship

But still I want something like will ruin every girl reputation

Find some dirt on one of them that will also cause a negative impact on the other.
For example, Lets say their names are Patty and May.
May is dating a guy named Bob.
Patty has a massive crush on Bob and is jealous of May.
Patty notices that one day May is sick, so she decides to make a move on Bob.
Bob gives in, and eventually they start to secretly date.
May finds out after you tell her, then screams at Patty, causing their entire friendship and love lives to be torn apart.