But no, he sucks

The story:

My friend really likes Arctic Monkeys and she was
playing them when we were hanging out once.

I'd heard this album a few times by then and I'd
gathered that most of it was about unrequited love
and I figured this song was so different, but
unlike the others it was written in second-person.

This lyrics to this song say something about
knowing who's calling but the number's blocked so
I thought it was about how the guy calling is
really good for this girl but she ignores him
because "he sucks."

One day my friend played a live version and this
line was sung clearer so I asked if it was "He
sucks" or "knee socks"...Turns out I was wrong...