Invest in a flask; something slim, and not too ostentatious. But don't drink from it. Instead, go with a college-era trick: use either opaque containers (like a disposable coffee cup) or ones that dissemble what the liquid actually is (certain lighter beers resemble apple juice). Then sip. You cannot grimace after each sip. Dead giveaway. And keep the sideways smirking with any coconspirators to a minimum.