10. Steve & Sharon's Kiss - Captain America: Civil War
For the entirety of Steve Rogers' MCU story arc, Peggy Carter was the love of his life, and the motivation behind so much of what he ever did. Even after waking up, he went to stay by her bedside in Washington, and was devastated by the news of her death.
He went so far as to sacrifice his life as Captain America with the Avengers, something that he always saw as his unwavering duty, to have a normal life with Peggy. She was all he ever wanted, which begs the question, why did he kiss her niece during Civil War?
Sharon Carter was introduced to the MCU during Captain America: The Winter Soldier, and apart from one conversation about getting a coffee, there was never any romantic connection between her and Steve. Out of the blue however, during Civil War, they shared a kiss.
Agent 13 was a strong character on her own, and there was absolutely no reason for her to become romantically involved with Cap. It wasn't like the moment was a catalyst for any further story or character development, it just felt forced and completely unnecessary.