You're Servant backhanded you for not wearing clothes. I don't think he's going to pass up an easy kill on a Master who's summoning was interrupting even if make the case for an alliance. 
This assuming that hitting the Master even interrupts the summoning. Shirou and Silver wolf didn't use incantation's, they just had the will to survive an oncoming threat that called forth their Servant. As Hector showed, you could just break out into song to summon forth your Servant.