Wearing a flag (or even a flag-printed shirt/pants) is not patriotism, it's nationalism and jingoism. It's also disrespectful of the flag per the US Flag Code (4 US Code § 8). If you don't like being criticized for being disrespectful, you have it in your control to stop wearing flag clothing.
Verdict: Don't get again, but don't turn it down if there's no other dark beers in the cooler. There's nothing wrong with the beer (well, besides the label) but there's nothing particular to recommend it either.
Humans do have a knack of choosing precisely those things that are worst for them - Harry Potter and the Philosopher's Stone, J. K. Rowling