The answer to 'grout grimy' is that grimy grout is a common problem in bathrooms and kitchens. It's usually caused by a buildup of soap scum, mildew, and dirt over time. Symptoms include discolored, stained, or crumbling grout lines. The good news is that there are several solutions to clean and restore grimy grout, depending on the severity of the issue.
For light grout cleaning, you can try DIY methods like scrubbing with a grout brush and a mixture of warm water and mild detergent. For tougher stains, you may need to use a grout cleaner or whitener. If the grout is severely damaged, you may need to regrout the area, which is a more involved process that's best left to a professional cleaning service.