Aisumasen (I'm Sorry) Lyrics

Lyric discussion by bee74 

Cover art for Aisumasen (I'm Sorry) lyrics by John Lennon

Aisu"i"masen is "I'm sorry" in Japanese. I guess he only speaks broken Japanese. I have no idea what "When I'm down, real sanpaku" means.
sounds like another japanese word, but not the one I know.