Why did Bil'am speak so abruptly to Balak "Kum Balak ... !"?
Why did he refer to him as "B'no Tzipor"?
Rashi #2 (24:3): He referred to him as his son, because he (Tzipor) was inferior to Balak in kingship. 3
Ha'Emek Davar (Harchev Davar Bereishis 48:8): It is humiliating to be called so, as if he does not have his own name (Rashi Tehilim 4:3). One who hates someone does not call him by his name. E.g. Sha'ul called David "Ben Yishai" (and was furious at Yehonason, who called him "David" (Shmuel 1:20:30). Bil'am says about himself "Bno Be'or" (24:3), i.e. in addition to his name. Here, "Bno Tzipor" is in place of Balak's name.