Harry has been living with Snape as his legal guardian for a while, and whilst he hasn’t been punished, clear rules haven’t been set either. Harry has not a single instance of survival instincts in his body, so he decides to start pushing boundaries with pranks(rip Severus I’m so sorry)
Now, knowing what he knows about Severus and his background with bullying, alongside Harry’s own background with it, he doesn’t want to do anything truly mean spirited. He also knows that Severus really likes his space organized and clean, so nothing that creates loads of mess either. He kept running into dead ends until Hermione gets back from her summer holiday in America.
She has obviously told him all about her trip, including visiting a southern style barbecue restaurant. There she had something “that cannot and should not legally be considered tea and is a disgrace to the people who enjoy tea everywhere in the world.” It was apparently a cold tea(?!) with heaps of sugar(?!?!). It was perfect for Snape.
The next couple of days were spent planning. Sev had to start brewing for the infirmary restock before the term started, which means he would be pretty busy. Harry graciously and innocently offered to help with cooking meals so Severus could focus on his invaluable work that Severus provides to all of the students and staff.
His brewing was almost entirely complete, and working tirelessly for an entire week had him exhausted. He was grateful for Harry’s Potter’s continued help with housework, although he felt slightly guilty for essentially being exactly like the monsters who had housed him previously. He had also felt guilty for his continued suspicion of the boy. He had been slightly too helpful, not complaining once, but every so often he would catch Harry smirking while staring at him.
His final potion was done and just needed to cool. He felt the bone deep exhaustion creeping in more and more, no longer be held at bay by the laundry list of tasks he had to complete. Merlin’s hairy fucking balls he needs tea, a drink, and a nap in that order. The sound of a door opening makes his head snap up; he sees Potter enter with a barely concealed smirk.
Harry: “Hello sir I’ve brought you some tea and biscuits since your brewing is done.”
Snape is automatically suspicious, spy’s instincts and whatnot but he decides to say screw it and drink the tea. He earned it and he was about 80% sure that Potter was over the horrendous way Severus had treated him. He lifted the mug to his lips and reveled in how nice the warm, smooth, and slightly bitter the drink in front of him was about to feel.
He parts his lips and welcomes the taste of his favorite, except the taste was all wrong. Why was it cold? Why did it taste like it had enough sugar to give a horse type two diabetes??? He spit it out immediately and started coughing.
Harry had a shit eating grin plastered on his face. He was desperately holding back peels of laughter.
Harry: “What’s the matter sir? Is the tea not to your liking?”
Severus: “That! That should not be considered tea! It is awful I can feel my blood sugar elevating!”
Harry: “It a new style of tea I’m experimenting with, it’s from the southern United States.”
Severus started laughing, honest to god full bellied laughs. This was so ridiculous; he was so tired, but he couldn’t stop laughing. He wanted to be mad, but just couldn’t bring himself to get angry like he should’ve been.
Harry on the other hand was absolutely freaking to fuck out.
Harry: “Shit, fuck, fuck, fuck, shit, fuck, I broke Snape! What do I do??? HEDWIG, HELP I BROKE SEVERUS”
This obviously made Severus just laugh harder, and he was having indescribable amounts of joy seeing Harry freak out.
Harry is traumatized at hearing Severus laugh. He decides that pranking is probably not a good idea for the sake of both their mental health. But hey, he didn’t get in trouble and honestly he didn’t quite mind that type of tea after working in the garden in the blazing British sun.