Oh, VERY nice! Very realistic. Very - dare I say it - mature. This fic is well written all the way through, but after the humorous setup (love the poisonous hydroflora! and the side snark about Snape having to ride a broom) it turns into a well-thought out depiction of how they might interaction in such a potential situation.
Their dialogue and actions and emotions are utterly evocative of Snape and Harry as believable, deep, and thoroughly human. I love how well you wrote this!