Why would anyone need to do this except to give others a false impression of their accomplishments? It's like a baseball player suggesting that he could remove from the record books all the times he struck out. We would all look perfect.
why you ask? I'll give you a good example.
http://us.playstation.com/community/mytrophies/ <---go there and search my online id PLYMCO_PILGRIM. You will see about 150 games show up on the trophy list. It would be nice to remove the few games I bought, tried, and didn't like so that I don't have those on there when trying to sync/compare with friends.