Sirius + Rosier (+ Gideon)(+Godric)
If Sirius hadn't been held back, he would've started to tear the stranger to bits.
"Let me go!" he snarled, teeth bared, hands clenched into tightly balled fists. "I'm going to kill this fucker!"
He still had to be held for several moments after the stranger had turned and walked away, lest Sirius followed and tackled him. When he finally cooled down, he glared in the direction which the stranger left, even though he'd disappeared into the crowd, and he adjusted his leather jacket.