1 of 4
1. DON'T DO THIS TO YOUR HAIR
Who was 'NSYNC's No. 1 fan? Clearly, not their hairstylist. But we'll blame the '90s for the bowl of ramen noodles that sat atop Justin Timberlake's head – not to mention the questionable looks sported by bandmates Chris Kirkpatrick and JC Chasez (who, along with Joey Fatone and Lance Bass, are rumored to be reuniting at Sunday's MTV Video Music Awards). One Direction's Harry Styles, Niall Horan, Zayn Malik, Liam Payne and Louis Tomlinson should go in a different direction and consider cleaner cuts, never in the yellow variety.
2 of 4
2. AMERICA'S SWEETHEART WILL BREAK YOUR HEART
When JT, then the face of our collective '90s teenage dream, romanced Britney Spears in 2000, it was a match made in pop music heaven. Until it wasn't, when they split two years later. Here's hoping Styles already got the memo after his swift relationship with the sugarcoated Taylor Swift went sour earlier this year after just a month together.
3 of 4
3. DON'T DISS YOUR FELLOW BOY BANDERS
The 'NSYNC vs. Backstreet Boys debate could come between the closest of friends. And families. And lovers. Yes, it was deeper than Team Edward vs. Team Jacob and even more dramatic than Team Angie vs. Team Jen. But 'NSYNC let their fans duke it out rather than get involved, unlike One Direction, who has called out fellow English-Irish boy band The Wanted in interviews and on Twitter. Sure, you can argue that 'NSYNC wasn't able to sling insults in 140 characters or less, but is there an excuse for someone – and we're looking at you, Zayn – suggesting that the competition has an STD?
4 of 4
5. SOME THINGS SHOULD REMAIN OFF THE RECORD
Unlike the boy bands of the '90s, One Direction doesn't always keep it squeaky clean. Case in point: Styles's stripper-filled 19th birthday celebration – and subsequent play-by-play to the U.K.'s Sun – might have been out of sync with their young fan base. What happened off stage stayed off stage for JT and his band mates, and that's something we can all sing along to.