Pissing off John Wick doesn't matter anymore. Viggo has already sent men to kill Wick, and even put a $2 million bounty on his head by the time he killed Marcus, so John is already pissed off (from Viggo's point of view):
Viggo tries to talk John out of seeking retribution, but John silently refuses. Viggo then sends a twelve-man hit squad to John's house, but John kills them all and has the bodies professionally removed. An unsurprised Viggo places a $2 million bounty on John's head and personally offers the contract to Marcus, John's mentor. [Wikipedia]
Besides, the plan Viggo had in mind by telling John Wick about it is to have Perkins ambush him:
Perkins sees that John and Marcus have been in contact and tells Viggo, who has Marcus beaten for information before executing him in his home. Viggo calls John to report this, planning to have Perkins ambush him. [Wikipedia]
But Perkins dies (get executed by Winston) before she could do so.