Yeah, I don't really watch "Phineas & Ferb" anymore, but I used to all the time, and I found this song title while scrolling through Instagram, and decided to revisit it on YouTube. Almost instantly, I was inspired to make this, and even made a little story to go with it:

Rarity, Pinkie Pie, and Twilight Sparkle are having a drink at Sugarcube Corner and the young princess explains that Rainbow Dash, her fiance, hasn't really been around lately and that she comes home late every night. Since she has never been in a relationship before Rainbow, she doesn't really know what to think about it. Rarity has been, however, and Pinkie is concerned for Twilight's well-being if it's what the two think is happening. So after sending Twilight home, the two begin their own little investigation, trying to figure out and prove that Rainbow is cheating on Twilight with somepony else. They find evidence to support their cause, and soon believe that it is the sad truth, but how to gather all the information and think of a way to tell Twilight? Sing a song about it!

Portraying Vanessa in this video is Rarity, and Pinkie Pie is playing Candance. I'll leave whether Rainbow is the cheater and/or someone wants to finish the little story up to you guys. I have no preference for the ending, really. I could see it go either way from what I put in the story and in the video. ;)