Not only did the movie manage to include a bass guitar in their promotional materials, but this interview reveals a monumental scene that no doubt represents the climactic height of the movie:
Brandon Routh: And I had to learn to play bass — both Michael Cera and I had to for our bass battle. I had to find out what looks cool when you’re playing the bass guitar.
The answer, Brandon, is that the mere act of playing bass guitar represents the coolest thing you can do.
Especially in a bass battle.
Without a doubt.