Keith goes up to Shiro one day after training and says “I think I’m allergic to Lance.”
And Shiro, bless him, is legit concerned like “What do you mean allergic? What’s wrong? Do you need medical attention?”
And Keith goes “Every time I see him I get heart palpitations and my face gets hot and my hands get sweaty. I think I should stay away from him.”
And he’s so fucking serious and worried that Shiro doesn’t know what to tell him so he just gives him a pat on the head and goes off to try to find someone more qualified to explain to Keith what a crush is.