Mmm... tastes like sanitizer
There are few things more attractive than a foam-topped ice cold beer, and few things are nastier than bubbles streaked down the side of your pint glass. Those bubbles that cling to the side mean that the glass in not clean. Instead of rising to the top, the carbonation gets stuck on the sides because of grime, dirt, grease or sanitizer (best case scenario).
Next time you’re pouring a beer, check for glass-cleanliness. If you see these life-ruining bubbles, DUMP IT and get a new glass. The money spent on dumping the beer is well worth it over watching a guest painfully drink from a dirty glass.