The look on someone's face when they are being a massive keeno and you have just said something demonstrating that you don't give a fuck. Tirfi stands for 'This Is Really Fucking Important'. It's the exact opposite of an idgaf. The working world is beset with tirfis and it is the job of idgafs to identify them and make them realise what work is really about - drinking tea and surfing the internet.
It's 9am and the tirfi has already been in the office for 2 hours.....
Idgaf: Has anyone seen the lunch menu today? I am fookin starvin...
Tirfi (with a disappointed look on his face): Have you not got any work to do?
Idgaf: You are such a tirfi mate, you need to chill out and make me a cup of tea.