When I first heard Bohemian Rhapsody as a 10 year-old in the 70s, the line, 'Mama, just killed a man', annoyed me as I thought his mum had killed the man and the singer was getting blamed for it. I remember thinking she wasn't a very nice mum.

Well the comma puts paid to that interpretation. Or maybe you don't understand commas?

What a pity Freddie couldn't have just added an "I" before "just killed". "Pulled my trigger" makes more sense then too, and "But now I've gone and thrown it all away", "Gotta leave you all behind and face the truth", etc (Comma visible, lyrics in last column in image)