"pek chek" means singaporean hokkien-influenced slang meaning frustrated, exasperated, or fed up — the feeling of being at the end of one's patience with a situation or person. It is one of many casual words teens pick up from friends, social media, music or sport, and on its own it carries no particular warning. If you hear your teen use it, it is fair to ask what they mean by it in their friend group, since meanings drift quickly. Asking out of curiosity rather than alarm tends to keep the conversation open and useful.