Being almost anal about details, meticulous, keeping everything neat and by the book.
“I had to count out each coin as the fastidious ten-year-old logged them in his notebook, five long minutes for a plastic cup of lemonade.”
Fastidious is frequently used to describe pedantic behavior. For example, if you’ve a very particular way of doing things that, if not abided, will cause mild distress.
“My husband was a fastidious critic of my dress, displeased with the slightest rumple or a color that did not match his shirt. Actually, he might’ve been autistic.”