There must be more to that sentence because it is a sentence fragment. I think with the rest of the sentence we might be able to better understand what it means. The previous answers given are true for what we know, though.

Hello, Kim Wi! To "crush" something is slang and it means to excel or master something. If someone has won a tournament or a game, you could tell them they crushed it. Here are some examples: 1. We Just scored 10 points. We are crushing the other team! 2. You did so good on the test. You crushed it!

The other answers are great. One extra note on the word "legitimately" used in this context... It's not needed at all. Many younger Americans use this word in places it really doesn't belong. When someone is talking with young people, most won't mind hearing the word "legitimately" in this context but in business contexts or speaking with educated people, if someone uses "legitimately" in this informal/colloquial way, many of them might judge that person as being somewhat ignorant and inarticulate. Use legitimately by its dictionary definition: "She has legitimately good reasons to be angry." TL;DR: At this time in the Western business/academic world, using "legitimately" in the informal/colloquial way sounds immature to many, so avoid it in those contexts.

The speaker is using humorous language. "In the grand scheme of things" means "the big picture" or "the whole world" or "all of history." "I am stuck in traffic and I'm going to be late. It seems important to me. Oh, well, in the grand scheme of things it's nothing." "Crushing this" is an informal phrase. It means accomplishing a task well. Figuratively, the task is like an enemy to be destroyed. "Crushing" the task means doing it so well that you have conquered or destroyed it. "I've gotten an A on every chemistry test." "Wow, you're really crushing it." "Legitimately" (note spelling) really means correct, authentic, valid, or legal. However, here the speaker is using it in an informal way. The speaker just means "really" or "truly." Here's a more correct use: "He won the Tour de France bicycle race." "Was it a legitimate win?" "No, he was using performance-enhancing drugs and they took his awards away."

Life is weirdly hard and sad and lame and cool and fun and messy and you have been through so much so much but you're still here taking it a day at a time and every single thing you thought you weren't gonna get through... you got through and survey says that's a pretty iconic ratio of success so don't forget to treat yourself today do something you love or eat your favorite food or just take a moment to stop and be like whoa holy ef.I'm legitimately actually crushing this because, in the grand scheme of things ,even if it doesn't feel like it. You are ( that all sentence)