One of my fights with BF before !

We have been fighting over 5 years, but one of fight was never forgotten and he learned some Chinese from here. 

He thought he knew lots things for China including some bad issues from China, I argued with him strongly and start to say" You think you know everything about China, actually, you know 个屁也！！！“ He said very quickly " Better than nothing!!! ". I could not control myself and start to laugh. He realized something wrong and ask." What does 个屁也 mean? " I explained, he felt embarrassing and fooled by me. 

Later on, he started to practice this word in many times to revenge me. 

He like to bring me to eat outside lots. One time,when I told him what want to eat, he said" You want to eat 个屁也“。 

He is such bad big boy!!!