When someone wishes you a happy birthday, the most common and appropriate response is to thank them. Here are some ways to respond to happy birthday wishes:

1. Say "Thank you!" in person or over text or social media.
2. Send a thank-you card or letter, especially if the person gave you a gift.
3. Reply to messages that go the extra distance. If someone posts a long, heartfelt birthday wish over social media, reply to it in person. Post a reply at least three sentences long.
4. If its from a family member, reply in kind and take the opportunity to reminisce about days past or start a conversation.
5. Use humor to respond, such as "Thanks for reminding me that Im one year closer to death!".
6. Let them know that their message made you smile and brightened your day.
7. Make them feel special and unique by saying something like "Thank you, I look forward to our adventures in the upcoming year".

Remember to respond in a timely and concise manner, and show your gratitude and appreciation for the well-wishes you received.