Yes, vinegar can ruin your grout. However, it happens when the grout is not sealed well, seeping into the air spaces within the surface. Below are ways vinegar ruins your gut.
Etching of the Grout
As vinegar cleans the surface, it dissolves through the grout finish lines, making it appear dull, and it eventually creates wear. If the wear stays longer, it spreads along the entire surface, which makes the floor look like an acid attack. The spread of the wear also affects marble, travertine, concrete, and terrazzo surfaces.
Vinegar pH Shift
Due to the acid nature of vinegar, it can change the PH level of a surface. As the pH changes, it reverses the reaction used to seal your gout, creating a different condition of the surface and reverting into a liquid form, which becomes ineffective.
Leeching Grout Dyes
Vinegar can leech out the dyes on your grout and lightens it, discoloring the grout with time.