I spent an entire year in an internship in the Brazilian branch of a multinational telecommunications company before I left for another internship in a local start-up. My manager was at his annual leave from the time I got an offer from the other company to the moment I actually left, so I never got to properly bid farewell to him.
With Christmas coming, the idea of gifting him and writing a little 'thank you' letter came to my mind, and I was wondering whether or not that could be considered inappropriate? Don't take me wrong, as much as part of me would love nothing more than returning to my old company, I don't think that would be possible, and even if it was, well, I feel like my old colleagues would think of me as some kind of traitor for leaving the company, so the only motivation behind this gift would be to thank him for being one of my mentors and perhaps for apologizing for letting him down like I did.