Just explicit enough is fine, there's a lot of sexy in suggestiveness as well, underwear being stretched thin down there hits just right for example.

Absolutely magnificent work, you've outdone yourself my guy, I hope you had fun making it.

Whatever you feel most comfortable with man, don't feel pressured to do something like this if you're not ready for it yet.

Happy bday Boo, have a good one!

Happy Birthday! Hope you have a good day today.