As you might notice ... Hailey is trending right now, and it all has to with stans of hers ripping into this innocent clip that Selena is featured in -- one posted by one of her good friends, Connar Franklin, who was the star at her own bachelorette party Friday.

What Twitter's bickering about now ... the fact Connar posted this video of her, Selena and other friends doing that catwalk lineup thing -- something Hailey also did earlier this month.

As you might recall ... Hailey and a bunch of her girlfriends pulled off a similar video during 4th of July weekend -- and it had tons of celebs in it, including Kim, Kylie, Kendall and Lori Harvey. BTW, this was Lori's video ... which is important.

Now, in the wake of Connar's vid -- which we suppose is kinda similar -- people (aka, Selena haters) are accusing SG of riding Hailey's wave ... suggesting Hailey would be slammed if the roles were reversed (namely, if Selena had done this first, and if Hailey had done it after). In other words, they're indicating there's a double standard at play in this ongoing dynamic.

What these "stans" fail to realize (or acknowledge) on both fronts is that neither video was carried out or posted by their respective idols -- they're both simply *in* the freakin' videos!

So, if this sounds like stupid high school s*** ... well, that's because it is -- and, in this case, the celebs themselves have absolutely nothing to do with it. Per usual, it's their fanbase that's running with BS ... trying to pit these two women against each other.

Funny enough, Selena had to call off her loyalists not too long ago -- telling them to back off of Hailey, as it appears they were dogpiling her during that whole "Mean Girl" thing.

She explicitly asked them to leave Hailey alone -- and Hailey thanked Selena afterward for speaking up on it. While their fans seem to think she's still bad blood between them, Selena and Hailey have, time and again, stamped that notion out ... and have even hung out.