It is pronounced 'Too-fis' and stands for 'Totally Up For it Sluzza'. The plural form of the word remains the product of endless debate, but 'TUFI' ('Too-fye') or even 'TUFISes' may suffice where there is more than one filthy cum-gurgling slut in attendance.
"I am so gonna smash that TUFIS in the salmon cavern."
"I think my mum might've been a TUFIS. How else do you explain my 10 half-siblings?"