Tile shower ceiling. Which is better to use, thinset mortor or adhesive/glue?

y'know, in 35+ years in the home decorating business, i have never seen a ceiling in a shower tiled, and there is a reason for this: the surface of the drywall will eventually fail due to temperature change and moisture (the constant wetting and drying) and tile will fall (perhaps on someones head). paint it with a good acrylic semi gloss or eggshell enamel...much easier to maintain