alt Hacker NewsGimp would have to be the extreme example of this. I used to recommend Krita to people, despite it being less appropriate for photo editing, just to avoid using 'Gimp' in work/polite scenarios.
I agree - "Birdy" is the name used with infants when talking about birds, or is a bird toy that photographers use to distract people ... which is a bit too close to the truth, perhaps.
To me it also suggests 'a toy version of Twitter'; and Twitter already had enough negativity around it for me.
Somehow I feel like GIMP's lack of popularity has more to do with its reputation for having a horrendous and impenetrable interface than its name.
At one point in the recent past there was a fork of GIMP named "Glimpse," yet weren't a sudden influx of users who were waiting for a more polite name.