People are strange...

There is a guy in my building who I’ve met many times and he knows my boss and my family really well.
Every time I walk past him in the building or in the street, I wave or say ‘G’day’ and he ignores me.
This morning I’m waiting for my coffee, I notice he is behind me. So I decide that this time I will deliberately ignore him.
I grab my coffee and as I am walking off, he goes out of his way to tap me on the shoulder and says “Morning Mate.”
I just don’t get people sometimes.