Hi. Here's a blog about the worst friendships on the show. This is only my opinion remember and you are free to yours in the comments section!I will provide a small explaination for each friendship.
Gwen and Courtney: the 3/4 of the friendship interactions is basically them fighting over Duncan.
Noah and Owen: not realistic at all.
Beth and Lindsay: Beth is kind of harsh towards Lindsay but on the other hand, Lindsay doesn't really look like she cares about Beth
Izzy and Noah: not realistic at all once again.
Cody and Sierra: why would Cody want to be friends with Sierra?
Duncan and Zoey: not realistic at all once again.
Gwen and Zoey: Same as Duncan and Zoey
Izzy and Leshawna: they are not friends anymore but they kind of were in TDI. Way too different.
Lindsay and Leshawna: Same reason as the one above.