But, umm

That pause filler phrase was part of the plot for the Jenkins episode of the TV comedy How I Met Your Mother that first aired in January. You can watch a brief video clip here.

I’ve never heard anyone but Robin say “but, umm.” Other common two-word fillers are “I mean”, “you know”, and “well, basically.”

Robin Scherbatsky is from Canada. She has a serious career as a TV reporter, but had a secret past as a teenage pop singer, Robin Sparkles. Perhaps the “but, um” filler replaced her former “eh”.

Robin meets some fans of her 4:00 AM cable TV talk show at a college bar. One of her friend Ted's students, Scotty, comes over to say that he's a big fan. She interrupts Ted's class to loudly announce that she is the host of the show. After she leaves, the class explains that they are fans only because her show comes on as their night of drinking is ending. Her "but...um" is the basis for a drinking game. Whenever she says it the students have to down a shot of liquor.

Ted and Barney try the game, and both get thoroughly drunk. After Robin continues to brag about having admirers, Ted explains the drinking game to her. That night, his class invites him out to join their game. Robin decides to fix them by repeating the phrase excessively. During the class the next day Robin startles the hungover students by shouting “but, um” through a megaphone.