DEAR MISS MANNERS: I am the hostess to two frequent houseguests (a married couple). They are delightful company and thoughtful guests, with one exception: They put their suitcases on the bed to pack and unpack. I have luggage racks in every guest bedroom in my house, including the one where they habitually stay, so there is no need for this distasteful and unsanitary practice. Can you please suggest a kind way to request that they not put their luggage on the bed? I find it easy to have the kinds of conversations that are house-specific (“These are the Wi-Fi credentials,” “These are the hours …