..is happen before

Hi

I’d like to ask you about the correct way to say that something happened before. I’m a bit confused since I recently was watching the following episode of “how I met your mother”.

http://youtu.be/lSAzC7ZmFjA

As far as I understand is Barney saying: “this is happen before” ( in sequence 0:19 sec ).

I thought it is said “this has happened before” instead.

Thanks for helping me.

kayano