Best girl syndrome is when someone feverishly believes that their favourite character in fiction (typically a female in anime, hence the name) is the best character and will be stubborn in saying that theirs is the best and everyone should like it, and that if they don't they simply say that they know them better and say that the other person is in denial, not considering the fact that other people have different opinions.
Guy 1: god I love insert anime waifu here
Guy 2: nah is insert different anime waifu is better.
Guy 1: fair enough, I just like mine better.
Guy 2: you don't seem to get it, they are better.
Guy 1: ...to you maybe, but I still prefer anime waifu1.
Guy 2: you just aren't giving them a chance! Stop being stubborn about it!
Guy 1: and you have Best Girl Syndrome
Guy 2: nah is insert different anime waifu is better.
Guy 1: fair enough, I just like mine better.
Guy 2: you don't seem to get it, they are better.
Guy 1: ...to you maybe, but I still prefer anime waifu1.
Guy 2: you just aren't giving them a chance! Stop being stubborn about it!
Guy 1: and you have Best Girl Syndrome
by Undert23 November 8, 2019
Get the Best Girl Syndromemug. The type of bitch that has a best by date on her forehead similar to a crash course bitch in many aspects a best by bitch is only good for a few days. Typically used for a place to stay, foodstamps, or welfare checks. Best by the 1st of the month.
"what happened bro I thought you were staying with Trish" "nah bro she was a best by bitch, I fucked her and stole her foodstamps"
by SlinkyDickTheOriginalSimp July 18, 2022
Get the Best by bitchmug. Becca is the best Jake stan ever. No debate.
She’s also the number 1 simp for Jake
So stan Becca the best Jake stan and the number 1 jake simp
She’s also the number 1 simp for Jake
So stan Becca the best Jake stan and the number 1 jake simp
by Best jay stan April 19, 2022
Get the best Jake stanmug. Said by people with Naturally Aspirated cars. Normally said by people with slow cars, and can't beat people in a race.
by 1v1IRL April 27, 2019
Get the NA is bestmug. 
On May 24 you must give your girl best friend/feminine best friend your hoodie to show how much you appreciate them
boy best friend: here’s my hoodie and happy
National give your fem Best friend a hoodie day
girl best friend: thank you so much you’re the best friend a girl could ever ask for
National give your fem Best friend a hoodie day
girl best friend: thank you so much you’re the best friend a girl could ever ask for
by DabiXhawks<3 May 20, 2021
Get the National give your fem Best friend a hoodie daymug.