For me, I am recovering from Social Anxiety Disorder. I find very hard to find positive things in any situation.
Are you sure it's all caused by the negative talkings in front of you? I think you just can have a correlation drew out of here, but not the causation. As psychic disorders are either a result of shocks and bad experience, like mistreatment or abuse in early ages OR they're genetically preprogrammed to occure, like two negative people (with their different brain chemistry) making a child (with their genetics 50/50 + some randoms).
Either it's the first one or the second - preposition is laid.
There are quite a lot people with mental disorders like depression and fears and compulsive behavior. Is it all because of bad talking? I don't think so. It's all together. And the social circle and the people in there matter too at certain point matter a lot for the mental health ..
You have to see success and advance, to accept and love yourself, you have to complete things so you can have positive experiences. This will give you self esteem and awareness - and that will change your brain and self thinking. Try to do a lot of sports - if you see your muscles grow, you will see success :)
Get professional help to assist you and explain your condition. Don't rely on one doc's knowledge, because there are a lot of people doing that work - but some of them should play in movies (better actors than doctors)
1. Try to observe people interacting on a daily basis.
2. Note the range and distribution of demonstrated behaviours.
3. Pick a reasonable cutoff (eg median or mode).
Now, whenever you see people behaving better than the cutoff —even if their behaviour is far from some hypothetical ideal— you are witnessing a positive thing.
[To answer your direct question: infrequently to rarely. Back in the last century it was believed that if one does not have anything nice to say it is better not to say anything at all. (and failing that, there were even backhanded circumlocutions like "bless their heart" which could be pressed into service)]