"My Dad was from Liverpool, and he picked it up in the army. He'd often come out with this stuff"

Mike Myers is referring to the phrase "things" which his daddy got while in the army. His dad was from Liverpool, and it is most likely that he was exposed to different cultures and languages while in the military. This might describe why he was able to get the phrase "stuff" and utilize it in his daily life. It is possible that the expression was utilized as a method to express something without having to discuss it in detail. It might also be a method of revealing surprise or disbelief. Whatever the case, it is clear that Mike Myers' daddy was able to get the phrase and use it in his everyday life. This might be a testimony to the power of language and how it can be used to reveal a range of emotions and concepts.