Methyl thiocyanate
Methyl thiocyanate is an organic compound with the formula CH3SCN. The simplest member of the organic thiocyanates, it is a colourless liquid with an onion-like odor. It is produced by the methylation of thiocyanate salts. The compound is a precursor to the more useful isomer methyl isothiocyanate (CH3NCS). Safety
The LD50 is 60 mg/kg (rats, oral). It is listed as an extremely hazardous substance by the United States's Emergency Planning and Community Right-to-Know Act. References 

Thiocyanates
Methyl esters
Foul-smelling chemicals