There are various reasons why Sonic doesn't like Rouge.....

Knuckles pov

I wouldn't say Rouge is absolutely good....I say she's a completely selfish and disgusting Bat..... Sensitive never liked her in the first place..... you won't believe how many beatings she took from him over the past 13 years..... ever since Sense was 4 years old he really saw me take a beating from Rouge..... from the moment he first laid eyes on her...he never liked her....not even one bit..... as soon as I was about to take another beating Sensitive just stood in the way and yelled, HEY YOU CAN'T BE MEAN TO HIM LIKE THAT YOU BIG FAT MEANIE!!! Rouge's eye widened with shock as he said fat.....I chuckled when Sensitive said that..... enraged Rouge said, WHAT DID YOU CALL ME YOU LITLLE BRAT!! Sensitive replied, YOU HEARD ME YOU BIG FAT MEANIE NOW LEAVE KNUCKLES ALONE OR I WILL MAKE YOU!!! Rouge said, and what are you going to do about it you little brat..... Sensitive replied as he kicked her in the face, THIS IS WHAT I AM GOING TO DO ABOUT IT YOU BIG FAT MEANIE!!! He kicked her so hard it was like 6 miles away from us......he turned to me and said as he pout, I don't like big fat meanies like that stupid bat being mean to you....Sensitive couldn't stand Rouge ever since..... he's actually kinda cute when he's all pouty like that.... I said chuckling, oh come on Sense loose the pouty face.... I started tickling him as Sense giggled that cute and adorable giggle he always had..... over the years Sensitive can't stand Rouge not even for one moment..... one time Rouge tried to steal the master emerald but Sensitive had other plans for her.... he yelled as he threw a rock at her hard enough for her to get away from it, DON'T YOU DARE TAKE THE MASTER EMERALD WITHOUT ASKING! Oh man he was mad I felt like Rouge was getting on his nerves rather than mine.... then one time after he turned ten years old he was completely ticked as he saw me get beaten by that bat...... Sensitive was ticked and said as he started beating her up, SHOW SOME FREAKING RESPECT AROUND KNUCKLES ONCE IN A WHILE YOU BIG FAT MEANIE!! He helped me up and then turned to Rouge with a really cold glare and said, listen here you big fat meanie....if you ever beat him up again I'll give you a nose bleed so bad that it can splash on your cloths and fur..... naturally I put it official he doesn't even like Rouge..... it was like as if they're fighting over me..... Sensitive was amazing compared to Rouge..... he maybe a guardian of an amulet but I felt like he's my guardian angel.....he was filled with life and light.... Sensitive always been there for me when I needed someone..... he may not admit it....but he had my back without even knowing.....but now I need to be there for him....I can only listen as he slept on my lap knowing he was heartbroken....and thinking it was his fault.....I kissed him in the forehead as I fell asleep myself....