It depends why they are envious. It could signify a lack of self-confidence in their own abilities. It could just be that they feel that life has done them down. It could be that they are going through a hard time in their own life. It could simply be that they are jealous.
Why someone is envious dictates how you deal with them. If the person lacks self-confidence, you boost their confidence. If they are going through a hard time, you know what to do. If they are simply jealous, you may want to see less of that person.
Another thing to consider is, someone constantly going on about his or her wonderful life, good luck, good fortune, great new job, new love new home or whatever, can be very galling and wearing if you have just lost your home, love, job or whatever.