Definition: In this task, you are given a Reddit post as a text. Your task is to generate a title for this text. The title should start with "TIFU by", followed by a situation that caused humor. The title should contain 7-12 words, ideally.
Input: Text: obligatory this happened a couple of years ago.

so, i was young and in high school and i knew this girl in my class, let’s call her rita, had only one arm. she would always hang sweatshirts or hoodies over her shoulder to hide the fact that she didn't have an arm. or maybe not hide it, but to help herself and those around her more comfortable with that fact..? not sure. but anyhow, one day i swear i saw a second arm. i thought to myself, hmmm this is weird, i could have sworn that rita only had one arm, but i quickly wrote it off as my being crazy and misunderstanding the actual purpose of always hanging a hoodie over her shoulder. 
in my head, rita now had two arms. 

here comes the part where i fucked up. one day i was feeling especially great about myself. now, rita and i weren’t very close friends but we were good acquaintances and i was feeling extra funny that day so, while rita is around me, i go up to her and bravely declare “you know rita, i used to think you didn’t have an arm hahahahahha how funny.” 

rita just looks at me, deadpan, and sternly replies “i don’t.”

my dumbass can’t believe how much of a dumbass i really am so to further add insult to injury i continue by stumbling across my words in an attempt to say something, anything, only to form the sentence “uhh..are you sure?”

“yes, i’m sure. i was born without it.”

“but, but…. i could’ve sworn i saw an arm there the other day!”

“no. you didn’t.”

i kept far away from rita after that. good thing we were seniors.

TIFU by thinking an acquaintance had two arms