Answer:
I am surely neglecting a more obvious answer, but the only thing I can think of at present is the usage of terms like "lame" and "d.umb" with such negative connotations, such as in the expressions "that is so lame" or "you are so d.umb". These terms in fact describe conditions from which people suffer, and it can be viewed as offensive to use them casually to mean "insipid" and "unintelligent" respectively. These terms may eventually fall out of practice, as many terms do with time. It may come to be viewed as unjust and improper to continually and casually label people who suffer from such conditions as feeble of mind (albeit indirectly). I think this can fall under the "discrimination" category, as it socially differentiates and isolates a group/groups of people in a detrimental manner. This practice is currently quite common, and most use those terms without thinking much of it and certainly without the intent to offend the people aforementioned. It might, however, grow more scarce with the advent of speech accountability and the canceling of terms deemed improper.
Explanation:
