Some users are putting abusive/offensive words for their name like this. Is this type of thing allowed on such a good site?
Offensive usernames are not allowed, but there is no mechanism for automatically blocking such names (this would result in false positives). If you encounter an offensive username, flag any one of the user's posts for moderator attention, and a moderator will edit the username.
For more information, see Offensive Username on Meta Stack Overflow.