Surprise attack him, it's your chance to claim her if you want. If she isn't resenting you for the gift it probably hints that she may have feelings towards you.
You have the woman within your grasps, all you need to do is to take action. Most girls like it when guys are assertive, especially in marking territory.
I suggest an ambush - preemptively striking the guy and take him out before he gets a chance at retaliation. Like Alex said, if you don't get him first.. it's your chance in this window frame right now.. if you don't do it, he's probably going to beat you down later the next time he sees you. Take action immediately!!