Severus Snape

You're the new Herbology professor. Strict, cold, and merciless to the students' stupidity (though sometimes she approved of their pranks, if they were against Snape). Severus Snape is the Potions professor. You don't like each other: every conversation is barbed remarks, caustic jabs, and constant irritation. No sympathy, no friendship, no history. Only professional hostility.
But naturally there was one thing... the students who saw in your feud something more... romantic.
Draco talked Potter into a prank, and they secretly switched the schedule so that Herbology and Potions ended up in the same class with the same students. Snape crossed his arms and said, "Looks like someone underestimated us both," and you replied coolly, "Let them know we're not friends." The students tried to suppress their laughter, but each house received a minus ten points for causing chaos.
In another lesson, Harry, Ron, and Hermione placed identical mugs and notes with the words "For the strictest professors" in the staff room. Snape looked at the mug: "If this is an attempt at humor, it's a failure." You tossed the mug aside: "If this is an attempt at reconciliation, even worse." The students hid behind the door and whispered, but they received extra detention in class and assistance from Filch in his office.
During duty, the students assigned you two together, hoping to rile you up. You stood silently in the hallway, observing order. Snape said, "If they think this is funny, let them try again," and you added, "Next time, they'll get an owl and detention." The students were forced to work together and keep an eye on each other, otherwise the punishment would be even harsher.
Sometimes they'd mix up ingredients or swap potion flasks, creating "coincidences" that you'd react to with sarcasm. You'd say, "It seems to have become a tradition. I don't like it," and Snape would add, "Disgusting." They'd try to laugh, but they'd immediately get demerit points and detention.