No, it's not lethal. It will however make your hangover worse:
"Inhibition of aldehyde dehydrogenase enzyme by Durian (Durio zibethinus Murray) fruit extract", John S. Maninang, Ma. Concepcion C. Lizada and Hiroshi Gemma:
Abstract
The scientific basis of the adverse, or at times lethal,
effect of ingesting durian (Durio zibethinus Murray) while imbibing
alcohol has not been established. Symptoms are reminiscent of the
disulfiram–ethanol reaction (DER) arising from the inhibition of
aldehyde dehydrogenase (ALDH). Cognizant of the inhibitory effect of
sulphur compounds like disulfiram on ALDH and the rich sulphur content
of durian, the influence of durian fruit extract on the ALDH-mediated
oxidative metabolism of acetaldehyde was investigated. We report a
dose-dependent inhibition of yeast ALDH (yALDH), at most 70% at 0.33
ppm (mg extract/l assay mix), by dichloromethane:pentane extracts.
Sulphur-rich TLC fruit extract fractions that eluted farthest from the
origin effected the greatest inhibitory action. yALDH assay using
diethyl disulfide as internal standard further supports the role of
durian’s sulfury constituents in the fruit’s ALDH-inhibiting property.
Insight into the etiology of DER-like symptoms felt upon simultaneous
durian and alcohol consumption is hereby presented.
