A phrase that comes from the show 13 Reasons Why- a show that follows the story of Hannah Baker, a girl that killed herself and explains why through 13 different tapes. This phrase basically means whatever you're using it in reference to was the final straw in making you want to kill yourself.
*sees a video of someone sticking their foot in a toilet with socks on*
Bro, if someone said this to, you fucked up. As in reference to the Netflix Original 13 Reasons Why, Hannah Baker made 13 tapes of reasons on why she killed herself. If someone said “You’re my 13th reason why” You fucked up and the person is saying you are a reason they killed themselves.
Me thinking: “oh i see my crush and it’s national hug you’re crush day, lemme go hug her”. Her: “why’d you hug mee?” Me: “it’s national hug you’re crush day” (october 14th- national give ur crush a hug day)