"Dammit dammit dammit!" Dipper muttered to himself, walking into the woods. She was at it again, looking for boys to date. Dipper snarled to himself as he found a rock to fume on. That girl, Mabel, HIS Mabel, alway looking for boys when the best one was right in front of her! He hated how she flirted, dropped hints, talk to boys, was AROUND other boys. It was worse when she gawked at them, hung up posters, read about them, just the thought of it infuriates Dipper. Every time he wakes up and sees those posters he wants to run over and tear them down. But that would show his secret crush, and Mabel would hate him, so he holds back. But barely.
It all started a few weeks before they arrived at their summer home. Dipper was inside playing his games, when he casually looked down the hall, and his eyes nearly burst out of his head. Mabel was taking a bath not a few minutes before, and she had forgotten to shut the door all the way. So, it had creeped open, and Mabel, realizing it was open, stood to get it. And right when she got to said door, Dipper had looked up. He at first was non-caring, he had seen his sister like this before, why should she bother him now? Whelp readers, puberty is a bitch. Dipper felt all the customary side effects of arousal in a few seconds time. The heart pumping, the blood rushing from his head to… his "other" head, the dizziness and the inability to look away. Mabel was like a hypnotist's watch, and Dipper, the unlucky hypnoty, was powerless to take his eyes off it until his line of sight was broken. And even after Mabel shut the door, there she lingered, in the back of Dippers eyes, glued to his corneas.
The rest of the day was a haze, Dipper was in a trance, one his parents explained as him playing to many video games, and Mabel saying he was crushing hard on a friend of hers.
You're half right, was one of Dippers only telligible thoughts in the whirlwind of emotions in his head. By the time they left for gravity falls, Dipper knew exactly what was happening to him. He was crushing on Mabel. Hard.
At first, Dipper tried to ignore his sister, trying to get over this silly crush. But no, the more boys she talked to, the angrier he became. He resorted to sabotaging his sister chances, destroying her notes, telling boys the shack was closed, he even told one that was actually interested that HE gave him the note. The boy turned on his heels, and left. Dipper watched him go with an evil smile. But it want enough. When Grunkle Stan sent him to hang up signs and he found 3, he came back to find that Mabel had found a boyfriend. Dipper played it off like he didn't care, but he was so enraged he had steam coming out of his ears. His claim of him being a zombie were only an excuse for Mabel to leave him. After seeing the fact that he WAS undead, Dipper flew to his sister, just as much out of worry as want. When he got there, she was attacked by gnomes, and, after the rescue, was relived that they where no competition.
When Gideon came into the picture, Dipper was infuriated. He went to the woods and stomped around for hours, only coming back a few minutes before her date was over. Dipper was a VERY good actor. After hearing his sister wanting to break it off, Dipper offered to break it off. After the fiasco of Gordon trying to kill him, Mabel saving them, Dipper realized that the only (and safest) way for his sister, was for him to, quietly, woo her. He experimented, adding a little spring in his step, wiggle to his walk, cuteness to his quietness, and, after all a weeks time, he saw his actions weren't going unnoticed. He caught her looking, glances at his face, his butt, even his crotch at times. She would always look away, and Dipper played it off like nothing happened. But he knew. It was working, slowly, ever so slowly, he was getting her attention. Just to play it safe, Dipper even pretended to be infatuated with Wendy, which in reality was also a way to try and overcome his attraction to Mabel. It worked, to an extend. But his sister was still on his mind.
When he screwed up at Summerween, he cursed himself, his plan almost ruined because of Wendy. He vowed not to put her first, which he already displayed at the fair. When he discovered that Robbie was hypnotizing her, he had a plot made with his Grunkles help, although he had no idea, and it went off perfectly, Wendy was angry at him and she left him alone. But the day after, his sister was at it again, trying to get a date. Mermando might still be her boyfriend, but Dipper was sure he could outdo the fishy bastard. And, here we are.
"I need to step up my game, this is too slow. She's bound to find SOMEONE who'll go out with her!" And then, an idea popped into his head. And that idea morphed into a plan. One so devious, ingenious, and complicated, it couldn't possibly fail! And so, Dipper went to work. Building one way, and fool proofing each part along the way. It was a great load of fun, but Dipper was soon finished. And all he had to do, was put in action. Laughing devilishly, he walked back to the shack. The master plan had begun.