It's a running joke wth the gang that Soda and Pony are a couple because when Dally first moved to Tulsa, he saw Johnny trying to pick up a battered and bruised Ponyboy off the ground, where the poor kid had been jumped. Dally instantly fell in love with Johnny and decided to help him out so he could date him. Long story short, they carried Pony to his house and when they got there, Soda went over and fussed over his little brother, kissing his bruises and saying he was gonna be okay and stuff like that. Then Dally said, "are the two of them dating?" Then everyone else started cracking up. Even Johnny was on the floor, asphyxiating via laughter. 

"What's so funny?" Dally asked, frowning.

"They're........ Bro...... Thers!" Wheezed Two-bit.

Dally went as red as a beat.