A/N: Ever noticed how Marty doesn't have anything with sugar in it? He always has Pepsi Free instead of the regular stuff, he refused to have any peanut brittle and he asked the owner of the cafe in 1955 for something "without any sugar in it". I've been wondering this for a while, and I've written this silly little thing.

….

May 17th, 1984

11:36am

Marty knew how he reacted when he'd had sugar, and quite frankly, for someone his age, it was embarrassing. He was fifteen, nearly sixteen, for goodness' sake! Plenty of people his age and even younger wouldn't react the way he would if they had sugar.

It wasn't that he was diabetic. He wasn't allergic to it, and he wasn't obese, so it wasn't for dietary reasons. It was something else.

"Marty? Can you pass me that wrench?" Doc called. The two of them were working on a project, an automatic dog-feeder for Einstein. If Doc ever had to go away for a few days, Einstein could still be fed without anyone needing to come round. It would save a lot of hassle.

Marty passed him the tool and continued working on the mechanism that would move the robotic arm. The idea was that, at a pre-programmed time each day, a dog-food can would be grabbed by the arm, swung round to the tin opener and opened. The arm would then move round and turn the can upside down, releasing the food into Einstein's bowl. The arm would finally swing round and discard the empty can in the trash before returning to its default position.

A little while later, they decided to take a break. Doc made them both a cup of coffee while Marty sat on the sofa, tuning his guitar. Doc had put sugar in both coffee cups without realising it and brought them over, handing one to Marty and drinking his own.

Marty didn't notice that there was sugar in the coffee. Although, once he'd finished the mug, it started to take affect. He began acting childishly, something that was rather surprising to the scientist. He looked up at Doc and began talking, his words coming out so fast that the scientist barely had time to register what he was saying as he was bombarded with Marty's speech.

"Hey Doc? I really should teach you how to skateboard some time. It's really fun and you don't have to walk anywhere, although you can't use it in malls and stuff or you get told off and these guys will come along and confiscate it which is really mean and it takes you ages to get the board back. For some reason they always target me even if I'm not using it they have some grudge against me and it isn't fair-"

"Whoa Marty! Calm down!" Doc put his hands up. "You're talking at a million miles an hour!"

"Am not!" Marty giggled. Yes, giggled. "I'm talking at a perfectly-normal-human-rate-of-talking. I have no idea what you're talking about!"

Doc hid the smirk appearing on his face. "You're talking way too fast, calm down,"

Marty seemed to find this funny, and got up, grabbing a wrench and running off with it. Doc rolled his eyes and walked after him, only for the teen to run around him to the other side of the lab, jumping over things.

Oh I know what's happened, the scientist thought with a smirk. He ran forward, trying to snatch the wrench back from Marty.

Marty only ran off again, giggling. He wasn't entirely aware of how he was acting. He jumped onto and over the sofa.

Doc smirked, sneaking up on him. He lunged forward and grabbed Marty's arm, pulling the wrench from his hands. Marty jabbed him in the ribs with a finger and he inadvertently let go, causing the teenager to run off again and this time he put on Doc's mind-reading helmet. It was huge, and Marty looked like an oddly-deformed mushroom when he put it on.

"Great Scott!" He exclaimed in a very bad imitation of the scientist. "This helmet makes me look like a complete twat!"

In retaliation, Doc took Marty's guitar and started playing it - very badly. It sounded as if the guitar had been in a horrific accident and was dying painfully. "Oh look at me! I'm Marty and I spend all my time trying to be famous but really all I do is skateboard around and try to be cool!"

"I'm Emmett and I spend all my time in a garage building useless pieces of junk because I'm so smart!" Marty started whacking the half-complete dog feeder with the wrench, clearly showing he had no clue what to do.

Doc snorted with laughter and began wheeling Marty's skateboard back and forth with one foot. "I'm always late for school and the teachers hate me but it's not my fault!"

Marty giggled again and took the helmet off, poking Doc in the ribs again. He laughed and ran off, clutching another wrench in his hand. Doc ran after him, smirking. He wasn't as fast as Marty, and that soon became obvious to the teen.

"Slowcoach!" Marty yelled over his shoulder, easily outpacing Doc as he ran around the lab.

Doc rolled his eyes and stopped running, watching as Marty stopped and caught his breath. If this was what the teenager was like after having sugar, he'd have to give him some more often. It was really amusing, especially considering the fact that the camera he'd set up in the corner for security purposes had caught the whole thing.

Marty threw the wrench onto the table and sat down, still panting. Doc raised an eyebrow at him, his arms crossed. "Had enough?"

Marty shrugged and went back to tuning his guitar, acting as though nothing had happened. "Don't be so immature,"

Doc scoffed. "Hypocrite,"

Doc had never expected Marty to be the sort of person to react to sugar in that way. Had he been six years old, it may have been normal, but at fifteen? That wasn't exactly normal behaviour for a teenager, although it was quite frankly hilarious.

And he had the video tape to prove it.