It was just an ordinary day at 221B Baker Street as John tapped on his laptop, creating a blog post for Sherlock's most recent astounding case solution. Sherlock, meanwhile, was on his own laptop, typing up something new on his website, though also glancing suspiciously at the door at frequent intervals. This scrutinizing of the entrance went on for about half an hour before John couldn't take the curiosity anymore.

"Sherlock, why are you doing that?"

"Doing what?"

"Glaring at the door like it's about to explode or something. You expecting a visitor?"

"Yes and no, see today's my birthday and-"

"WHAT?" Sherlock's sentence was cut short by John's exclamation of surprise. "Today's your birthday, why didn't you tell me?"

"Because, as I was about to say before your outburst, I have enough on my plate with Mycroft knowing it's today." Sherlock looked like he was about to say more, but a knock on the front door stopped him. "I'll get it," he said moodily, trudging down the stairs to see who the birthday visitor was. John smiled and returned to his blog, wondering if he should celebrate his flatmate's birthday somehow. He considered throwing a party with Greg, possibly inviting Donovan and Anderson just to piss him off, but before he could text Lestrade he heard a very, very high-pitched scream from downstairs.

"Sherlock, what's wrong-" but his friend ran past him in a surge of fright and slammed the door to his bedroom closed before John even finished the question. He looked to see what had scared the unemotional Sherlock so much, but in his rush the detective had slammed the door behind him, blocking John's view. The doctor briefly debated whether to open the door and see, or go comfort his friend, but Sherlock won out and he briskly walked to the man's bedroom door before knocked on it a couple times. "Sherlock, are you OK?"

"Go away, John. You might have that thing with you."

"Thing? What thing? Who was at the door? What did Mycroft send?"

"A clown." Sherlock might have said more, John will never know because at that moment he had to hurry to hide a snort of laughter. He didn't do very well though, and the door opened just a crack to reveal Sherlock's sulking face. "It's not funny."

John resisted the urge to say, "yeah it is," and instead simply asked, "Clowns? Why are you afraid of clowns?" but seriously, this was the man who had claimed in the Baskerville case that when he had seen the hound was the only time he had ever been scared, and yet, here he was, hiding in his room from a fat man wearing makeup and handing out balloons to children.

"Clowns make for awful deductions," said Sherlock. "They hide the part of their body that tells me the most about who they are, their face, by covering it with makeup. When around one, I don't know if it wants to hug me or stab me, and neither option is desirable. Furthermore, the rest of their outfit is a costume, not their actual clothes, meaning I can't deduce anything from that, either."

John could see where Sherlock's fear was coming from now. Clowns took away his best ability, deducing things. He was about to tell Sherlock he understood when there was a knock on the door to their flat, causing Sherlock to squeal and slam his door shut. John couldn't hold back a burst of laughter this time as he made his way to the door.

"Oh, hello Mrs. Hudson." said John, upon opening the door to reveal their landlady.

"Hello, dearie. Do you and Sherlock have a case?"

John frowned in confusion. "No, why?"

"Well, I heard that little girl scream downstairs a while ago, and I just assumed-" but she didn't finish her sentence as all the absurdity of Sherlock's phobia finally caused John to burst into laughter, gripping the door frame to hold himself upright. Upon explaining that the little girl downstairs was actually Sherlock screaming at a clown, Mrs. Hudson slapped her hand over her mouth to hide a smile and asked John to wish Sherlock a happy birthday for her. John said he would and waved as the woman retreated down the stairs back to her own flat.

Sherlock refused to come out of his room for the rest of the day, which John didn't really mind. This would mean no unprecedented experiments or new body parts in the fridge for a while.

The following morning Sherlock was back to his usual business, only now pouting slightly. "Hey, don't worry," said John in an attempt to cheer his flatmate up. "At least now you have a reason to get revenge on Mycroft."

"Oh, don't worry," said Sherlock, not looking up from his microscope. "Mycroft's birthday is not far from mine, and he just so happens to have a phobia of his own."