After that he understood the Headmaster's reasons, though it still stung.
No, his frustration stemmed from multiple sources, all of which were fanning the fires of his unpleasant nature. Being unable to get the Defense position was only a minor factor in that.
First of course was the fact that he didn't like teaching younger children. He could live with the older teenagers, as they understood what was expected of them, but the general ignorance of the younger students in anything potion-related clashed horribly with his own perfectionism. He simply did not have the patience to explain every little detail to children - after all, he got it all without any help in his own school years, so why shouldn't they? Using himself as the yardstick of course put the bar way too high - but he hadn't realized that yet.
His personality was not helping as well, and it had only taken three months for him to get a really bad reputation as a teacher from the students - especially from the older ones who saw him as lacking compared to Slughorn. He had not expected anything else however.
What he hadn't expected, was, how things were turning out in his relations with House Slytherin. At first he'd held high hopes in becoming the head of his old house at Hogwarts. However, things did not turn out as expected, as he was starting to understand.
Some transition problems had been expected - after all, Slughorn had been the Head of House Slytherin for over 40 years - thus why Slughorn had already introduced him and eased him into the job the previous school year. Yet, that was not the core reason for his current problems with the Slytherin students.
No, the core reason was, that the Slytherins didn't respect him. Oh, sure, on the outside they showed him all the respect his position demanded, but he knew the true nature of his old house, whose students have cunning as one of its required traits (though sadly there were more and more exceptions). He did have his own sources, and managed to puzzle together the mosaic of what exactly was going on.
Essentially, the older Slytherins had several reasons that they didn't take him seriously. First was his young age. With just barely over 20 years in age, he was not that much older as the students, and they thus naturally saw him as inexperienced and a pushover. Second was his tendency to be highly biased in favor of Slytherin, which had convinced them that he would never dare to move against his own house. Third and final, him getting cleared of all charges had had the unfortunate effect of poisoning the children of blood-supremacists and Death Eater sympathizers against him, as their parents saw him as a weakling or partial traitor.
No, this was not turning out as intended. He could not even flee into his private hatred. James Potter was dead, and instead of satisfaction, it had just left a void in him. Combine that with his guilt that it was his own fault that Lily was dead, and his life was pretty miserable.
Snape shook his head and returned to the task at hand, namely checking the potions of the first-year students, now that they were done. The potion was something so incredibly simple, even they couldn't mess it up - though that was daring fate to prove him wrong. While he knew the current Slytherin first years were still respecting him, this would soon change under the influence of their older peers.
Looking at the cauldron of one Gryffindor first year boy with striking red hair after several dismal results from others - even from his own house - he raised an eyebrow at the perfect color and consistency. "Have you practiced potions in private, Weasley?"
Bill Weasley was quite nervous when being addressed by Professor Snape, having already seen in class how nasty he could get. "My mother let me make some simple ones at home."
"Finally someone in this class who uses his brain." Snape saying this about a Gryffindor was rare enough.
"Man, you have no idea how lucky you just have been," the student next to Bill whispered after Snape had left.
"Actually, I do have a really good idea about that..." After all, Bill had felt like a game animal about to get shot.
Snape moved on to a Slytherin girl and could only shake his head. Even with his bias to his own house, there was no way that potion was anything but a complete disaster. Another dismal showing of his own house. It felt insulting to him, that the best potion up to this point came from a Gryffindor. It made him wonder how far his house had fallen since his graduation.
Having found an outlet for his bad mood, Snape drew his wand. "This is just plain horrible and I won't tolerate such in my classroom."
Watching Snape vanish the potion of the girl, who promptly dissolved into tears, Bill Weasley realized how he had just avoided a major point loss. Boy, Snape seems to have a relatively good day. I don't ever again want to experience another of Snape's really bad days...
After all, the one time had been more than enough.
...Nurmengard prison, Germany, May 8th 1984...
Nurmengard was a testament to the world of Gellert Grindelwald. It looked a lot like a medieval fortress, built in an inhospitable area of the German Alps, that looked straight out of an old fairy tale. It also was a stark contrast to present-day's magical Germany. However, Albus Dumbledore had litte eye for it while waiting at the main gate to be admitted.
"Alles in Ordnung. Sie können passieren," the uniformed guard said and gave back the magically signed papers. The big gate of Nurmengard opened for Dumbledore to enter, so he could visit its sole prisoner.