WTF?! Lindsay Lohan & Sam Ronson fight over a guy!

As pressure builds between the Sapphic duo, Lilo & Sam nearly exchanged blows after a high-pitched scream feast!

The two were at a posh London nightclub when Sam saw Lilo grinding with ex-luv Calum Best.

Ronson went psychotronic, fists flying at her busty GF before Best intervened, according to two UK tabs The Mirror and Sun.

Lohan flipped out, "screaming and kicking" as the two had to be pulled apart.  As they separated, Sam smashed a glass to the floor, shattering it.

Why the catty histrionics? Lohan was canoodling UK bad boy Calum before going lez with Sam.

Nether has commented via their respective MySpace blogs and Lohan's rep didn't deny the catfight stating, "I don't know as I wasn't there."