In the series Hitman Reborn Gokudera says this phrase over 520 times in the anime version to Tsuna (The 10th Vongola Family Boss).
This shows how much he respects him.
(Or can be seen as him being obsessed with Tsuna)
' Juudaimei !' / ' The Tenth! '
Gokudera talking about or to Tsuna:
' Juudaimei... ' / ' The Tenth... '