Mac wasn't so caught up in flirting that he didn't notice the man heading towards them. Anyone else might have missed it, but Mac was trained to notice when he was being stalked, and right now the hairs on the back of his neck were standing at attention.
He narrowed his eyes, and automatically changed his stance from relaxed to on alert. His wand had already been in his hand, but now he gripped it firmly but loosely, as he waited to see what the man heading towards them would do.