Both are acting pretty immaturely, if you ask me.
Not All Right
"Thanks," said John once Sherlock's classmates were gone, holding up the umbrella (a jazzberry pink one, courtesy of Mycroft). Sherlock was looking at him oddly. John frowned.
"Right," said his flatmate, turning. "I'll just head on home then…"
"Now, wait a minute." John vaulted himself over the counter and snagged Sherlock's shoulder. "I thought you said you'd walk home with me."
"It's quite all right." Sherlock sounded completely cool and at ease, but John knew something was wrong. "See you at home."
"It's pouring rain out there! Sherlock, just wait, we can walk together. Please?"
But Sherlock had already left.
Prompt was #82: jazzberry