Lyric discussion by cellotapetor 

Cover art for White Collar Boy lyrics by Belle & Sebastian

I also think it's "spit in your gin". It definitely sounds like "in", not "on", hence gin and not chin. Gin goes with the whole white-collar thing, too.

Lyric Correction

I'm not sure gin is correct. Their official site has it down as "spit in your chin." Though that doesn't make much sense either.