I like to visit a coffee shop on the quiet side of Mong Kok sometimes called Knockbox Coffee Company. They’ve got a cozy atmosphere and a good selection of gourmet coffee. I like to get their Ice Long Black (凍黑咖啡) for HK$31.
Knockbox Coffee Company
G/F, 21 Hak Po Street, Mong Kok, Kowloon, Hong Kong (Mong Kok MTR Station, Exit E)