Caffeine has been shown to have benefits for overall cardiovascular health. Plus, the caffeine positively affects the penis--here's the biology:
Why would caffeine prevent against ED?
Caffeine is known to affect blood vessel function, which the authors suggest is the likely mechanism for its effects on ED. They write that the “suggested biological mechanism is that caffeine triggers a series of pharmacological effects that lead to the relaxation of the penile helicine arteries, and the cavernous smooth muscle that lines cavernosal spaces, thus increasing penile blood flow.” In other words, arteries and smooth muscle relax, blood flow is enhanced, and the “cavernous” space in the penis that contributes to erection fills with blood more easily.
There are far more evil "lifestyle" contributors to ED like being overweight, being sedentary, poor diet, low self esteem, and stress.
Coffee isn't even on the map.