It's your boy's birthday dinner, so you go to show love. Once seated, you conscientiously study the menu for several minutes and decide that you're going to order water on the rocks (free) and a side of fries ($10 max.) At the end of the meal, the check comes and folks want to split the check evenly. Filet mignon never touched your plate and you refused that glass of sangria, but you're expected to pay for things you didn't enjoy?
Skip the "splitting the check" hassle and tweet your boy "Happy Birthday" next time. He'll retweet it—that serves as proof that you care—and you won't be responsible for sponsoring other people's indulgences.