I'd heard the song many times, but was never familiar with the slang...
Taken from http://rollingspoon.com/eat-beat-butter-tarts/
This post ignores the context. Butter tarts are indeed a popular Canadian pastery. The phrase butter tart, as used in the song, is also slang for a woman’s parts. Just like when the girl sings “my sticky paws were into making straws out of big fat slurpy treats” she’s referring to making the male equivalent, in big and thick form, shrivel back to a smaller size after extended attention from her hands.
In other words, they’re naughty lyrics not meant to be taken literally."
kinda makes me like the song less...
meh...
Or a more positive interpretation from http://blogcritics.org/single-review-len-steal-my-sunshine/
Sharon explains that she was napping on a bench in the park. She was playing with her slurpee and making thin straws out of she had left. People gave her weird looks, observing her weight and making fun of her as she created frozen soda straws.. People didn’t want to be around her. She pouts that it was lonely pigging out by herself.