Kitty, I hope you're not winding us up (but I must admit I DID have a bit of a laugh!)
There isn't a department store called IMHO - those initials stand for In My Humble Opinion. Mark says that the department store called "Central" is the best in Bangkok (others might suggest Siam Paragon .. same area, while others would nomiinate Emporium in Sukhumvit).

There are a few Central department stores around Bangkok, but Mark means the one in Chitlom, right by the BTS. That''s the nearest one to Siam Square.
Enjoy the shopping.