Green’s Dictionary of Slang

coffin nail n.2

also coffin screw, coffin spike, coffin tack
[? no more than the resemblance of the cigarette to the nail; nicotine’s cancerous potential is very much a phenomenon of 1960s+]

1. [late 19C+] a cigarette; occas. a cigar (see cit. 1945).

2. [1910s] (US campus) one who smokes to excess.