How I Met Your Mother Season 3 Episode 4: "Little Boys"
Robin is dating a single dad and ends up forming a close bond with his son. However, when she decides the relationship is too serious, she needs to find a way to end her relationship with both the father and his kid.
Robin: What's my "but"? You know, I'm really nice, but... Ted (voiceover): But she's afraid of commitment. Lily (voiceover): But she's a gun nut. Barney (voiceover): But she's... Canadian. Marshall (voiceover): But she doesn't like Field of Dreams. All: I can't think of anything.