I know I do because I find that it blurs the distinctions between the decades like say for example the 1950s, 1960s,1970s,1980s just to name a few-examples because the last-century is when decades started forming they're own distinct-identities unlike say decades in previous-centuries due to the faster-moving changes like technological-changes, changes in fashion as you start advertising them more easily and so saying the term 20th Century acts as if decades from that century we're no-more distinct than say 14th or 15th Century decades just as examples. I similarly find the term 21st Century problematic and confusing as well for that very reason mentioned above. How about you though personally do you find it bothersome when people use the term 20th Century? Why or why not?