Very easily if you allow them, especially if they have a low self esteem as well.
It can be within their nature to do so and most times they may not even be aware of it.
On the other hand, if they have a very high self esteem you may be the one negatively affecting your own through peer pressure.
It really boils down to your own attitude:
I try to hold positive thoughts daily: instead of the glass being half empty, I consider the glass to be half full.
Maintaining an 'Attitude of Gratitude' !