Use when blending in is not desired but happens due to awkwardness. After his voice cracked, John wanted to blend into the woodwork.
Pro Tip 2/3
Not Literal
Remember it's a figure of speech. No one actually becomes part of the woodwork. When I dropped my tray, I wished I could blend into the woodwork.
Pro Tip 3/3
Temporary State
Often used for a temporary desire to disappear in a specific situation. He blended into the woodwork during the awkward conversation but later joined in.