Direct answer: It’s generally more appropriate to say “Thank you for your service” or “I appreciate your sacrifice” rather than “Happy Veterans Day” when addressing someone who is currently serving or who is a living veteran. The phrase “Happy Veterans Day” is often considered mismatched with the solemn purpose of the day, which honors service and sacrifice. If you want to acknowledge someone actively serving, a simple “Thank you for your service” or “I’m grateful for what you do” is a respectful choice. If speaking to a veteran, you can say “Thank you for your service” or share a personal note of appreciation. Context and options:

• To someone actively serving: “Thank you for your service” or “I appreciate your sacrifice.”
• To a veteran (living): “Thank you for your service” or “I’m grateful for everything you’ve done for our country.”
• If you still want a warmer phrasing, you can say “Happy Veterans Day” in a casual, lighthearted way only if you know the person personally and you’re certain they’ll receive it positively; otherwise, stick with gratitude-focused language.