This is almost trivial, but I tend to use mouthwash when I wake up. However, the chemistry of the mouthwash leaves a stark aftertaste that will alter the flavor of food and drink I consume afterward--especially things like citrus. Thus, the first few bites or swallows of whatever usually wind up tasting rather foreign.
O, the gustatory costs of oral hygiene...
Related: Not quite a frustration per se, but a curiosity borne of bemusement is the fact that many mouthwashes on the market aren't nearly as effective as ones like Listerine. Why do people even use them?
