What does the author mean by:

"considering that his cheek bones were glistening with Mr. Bramble's buttered toast, were in poor taste"???

 Percy was talking against people of wrath. His comments were not pleasent to hear. When we eat something or tell something that we feel good, our face looks good (that is what authour means by cheeck bones glistening). The authour was telling that Percy liked all what he said and even though the butter toast was not good, Percy's cheek bones were glistening.