Final answer:
The real Snape-themed chapter title is "Snape's Worst Memory".
Step-by-step explanation:
The real Snape-themed chapter title is "Snape's Worst Memory". This is a chapter in the book Harry Potter and the Order of the Phoenix where Harry sees a memory of Snape during a class.
"The Sacking of Severus Snape" and "Snape Victorious" are not real chapter titles in the Harry Potter series.