Research studies on rats, trying to link peppermint and spearmint teas to suppress the male sex hormone, androgen, have proved inconclusive. This is a myth and there is no medical research to back it. Mint DOES NOT cause erectile dysfunction. Mint tea, in itself, or as part of an herbal infusion is recommended as an aphrodisiac in many ancient cultures and medicines.
Smoking menthol flavored cigarettes or eating mint based candy was mired in a similar negative propaganda. But apart from the ill effects of smoking (irrespective of the flavor) and the excess artificial sugar in candies (not forgetting the rest of the artificial flavors) on overall health, there is nothing to tie these directly to impotency or erectile dysfunction.