TLDR : Apparently there is no concrete proof of the drink existence.
Most of the references go around to The Dedalus Book of Absinthe or a citation in BBC1 documentary called ‘The Rise and Fall of DDT’ from 1974.
Someone did most the work for me, apparently :
the myth of the mickey slim
and this what I think may be the origin of the mith:
George Campbell, who helped initiate DDT production in Britain, said:
‘In American bars, there was a drink, called Mickey Slim. If [sic] was
a good gin with a spot of DDT in it, and this was supposed to give you
a feeling of happiness and merriment. You can see this in the
behaviour of flies if they are subjected to DDT. Their first effort is
to fly about, as though they were full of the joys of the spring, and
then they gradually die off.’”
- “Out of the Air.” Listener [London, England] 12 Sept. 1974: 332.
as a sidenote, I would like to point you to this.
is absinthe hallucinogenic