Just had to add (since I'm a giant Barbershop Geek in addition to all of the other ways I'm a geek ;))...

Lest anyone think that barbershop is just for old folks: https://www.youtube.com/watch?v=XWmFfFx24zs (Vocal Spectrum, 2004 international collegiate quartet champions and 2006 international quartet champions)

Or just for Americans: https://www.youtube.com/watch?v=rFWhnOP_UVk (Ringmasters, 2012 international quartet champions, from Sweden) https://www.youtube.com/watch?v=T6HM-oLG_cI (Musical Island Boys, 2014 international quartet champions, from New Zealand)

Or always serious: https://www.youtube.com/watch?v=ihdtI0E_mmQ (Storm Front, 2010 International Quartet Champions and comedy quartet)

Or just for men: https://www.youtube.com/watch?v=tWqtFxW4kiE (LoveNotes, 2014 Sweet Adelines International Quartet Champions)

Or just for adults: https://www.youtube.com/watch?v=sREQu_AaUso (The Osmond Brothers... yup ;))