Green Day's music is as simple as it is catchy. And because the pop-punk trio rarely strays from its three chord formula many of their songs sound an awful lot like other songs.

Our friends at Diffuser found 13 instances of a Green Day tune that sounds just like another song. But lest you think Billie Joe and the boys are being accused of plagiarism, in a bunch of the cases it was the other songs that came out after the Green Day effort was released.

Some of the matches are pretty well known. Like, for example, the Green Day song 'Warning' bares a striking similarity to the 1968 Knicks' song 'Picture Book.' (Which is a tune you probably know from the HP printer ads that were all over TV about five years ago.)

But one of the matches Diffuser unearthed we'd never really noticed before, despite it being near and dear to our hearts. It turns out Green Day's 2009 song '21 Guns' has parts that evoke the opening theme to the TGIF comedy 'Full House.' Compare the two songs below and let us know what you think.