Negative + Negative = Positive

Today at work I accidentally discovered that if you take two two-word phrases that mean the same positive thing and accidentally mix them up, it's two negatives.

I was talking to a lady on the phone and she thanked me. I got tongue-tied and mixed "you're welcome" with "no problem."

This is what I ended up saying to her: "You're problem. Err, no welcome."

I sounded like a total scrooge. Haha.