The definition of the term "flirting" according to Dictionary.com is: "to court triflingly or act amorously without serious intentions; play at love; coquet." Because there's no "serious intentions," does that necessarily mean that there's no harm in flirting when you're already in a serious relationship?
To some, the dangers of flirting are obvious. Others see flirting as a harmless rite of passage. The popular saying "I'm married, I'm not dead" simply gives justification to flirting with someone else when you're already in a committed relationship. So does that render people who feel they need outside attention immune from culpability? How does the spouse or significant other feel when they see or discover that the person they love is showing affection toward someone else? If the relationship they are in is troubled, hurt runs deep.
Some reasons for flirting are: lack of self esteem, a problematic love relationship, excessive inebriation, the need to feel accepted and noticed, etc. These personal reasons are usually deeply imbedded in one's psyche and only surfaces when there's a boost of confidence brought on by alcohol consumption, for example. Under sober, normal circumstances, flirting is not characteristic behavior that becomes public.
Flirting becomes very serious when careers are ruined. According to a CNBC report: "Former Hewlett-Packard Chief Executive Officer Mark Hurd was forced to resign in August 2010, after an investigation of a "close personal relationship" with a female contractor revealed that he had made improper payments to the woman." In most cases, seemingly harmless flirting becomes a vicious wheel that starts slow and picks up speed until everyone involved crashes and burns. Is flirting worth losing a Fortune 500 CEO salary?
People seek approval in various aspects of life. If you're already in a committed relationship, it is 100% acceptable to flirt with your significant other. Seeking outside attention through sexual enticement causes trouble for all people involved. A good test is to see how it would make you feel if you had to watch someone you love deeply flirt with someone else. Things usually begin to make more sense at that point.