This word is most common phrase of someone being themselves. No matter how much it’s used. It means it’s their thing and they just being themselves because they are showing how amazing there personality is.
Thalia: Lol
Simon: Oh yeah that’s your thing, and I love that you say that. It’s cute.
A text response, when you are too lazy to actually express how you are feeling or when you don't think somethings funny but you don't want to hurt their feelings.