I supect smells only affect the olfactory system and your mental reaction to it. Smell isn't going to kill directly unless your mental state uses it to trigger something.
Of course if you smell poisonous gas that's another matter.
if you wonder if there air born poisons then the answer is yes
( cyanide spring to mind)
what about hydrogen sulphide ? smells like bad eggs
is toxic in itself and could kill by oxygen exclusion
phosphine ( PH3) that is one up from ammonia NH3 is pretty toxic - there is a scene from this in Breaking Bad which gives you an excuse to look at them all again.
Group V elements all form hydrides which smell pretty foul and are toxic
Stibine SbH3 and arsine AsH3 - the last one could give you and your frenz hours of innocent amusement....
( there isnt a smell that can kill you by smell alone - as OG says you are hard wired so that doesnt happen - Olfactory nerve (I) frontal cortex has no connection with any part of the heart stopping bit or vagus nerve ( X ) hind brain.... )
Requiem for 2014 - which had a few case histories from the 10-40 thousand gun related deaths - a few of the shooters had shot their siblings for much less than not washing ....( 15 -38 in the UK - no not thousand )