Wugum (?!)

This has happened at least three times during the past week. I do something for a complete stranger -- such as holding open the door behind me -- to which that person responds with a "thank you". As is dictated in such cases, I in turn reply... "wugum." Wugum? How is it that what my brain perceives as a clearly encoded directive to utter "you're welcome" comes out so garbled? Okay, repeat after me are-tick-yoo-lay-shun.