"Not know whether to laugh or cry" usually means (to me) a situation is both funny and sad. Like you wouldn't say "my entire family was killed in an automobile

"Not know whether to laugh or cry" usually means (to me) a situation is both funny and sad. Like you wouldn't say "my entire family was killed in an automobile crash, I don't know whether to laugh or cry," there's no humorous component. Like you said, birthday cake celebration of an outgoing employee is neither.