The Shop Around the Corner
(1940)

Kralik (James Stewart) and Clara are romantic penpals but in real life work at the same store and hate each other. At their supposed first rendezvous, Kralik realizes that his special penpal is actually Clara. He approaches her and tries to tell her in a roundabout way that he's actually her penpal but she is so rude to him that he walks off. A few weeks later Clara has taken a leave of absence from work because she is so depressed that she was "stood up" by her penpal. On Christmas Eve she's back at work at the shop and she talks to Kralik about finally meeting her penpal. Kralik teases her a bit before finally revealing himself as her penpal. They realize that they have been in love all along and kiss.

Thanks Ivy!