It happened at least once to every teacher; the laws of probability demanded it, given the sheer number of students. Being under thirty helped, too.
Karkaroff picked up the sixth year's quiz with uncharacteristic delicacy and stared at the tiny scribbling in the margins. His Romanian was admittedly a bit on the rusty side, but it didn't take a fluent speaker to understand the meaning of his own name surrounded by lots of little bubbly hearts.
Just because statistical odds ensured the emergence of at least one student crush didn't mean he knew what on Earth to do about it.