It doesn't matter what kind of relationship I have with someone... friends, lovers, family... there are some things that totally ruin my trust. For me it's when someone tries to be hurtful to me on purpose. Some people have a bite to them and they like to lash out when they don't get what they want, and try to hurt you somehow, verbally or otherwise. When I can tell someone is like that I know it's time to part ways, cause it'll just keep happening. Not everyone is like that. Some people might get defensive and say or do something hurtful, but not because they're trying to on purpose. There's a difference there. What ruins your trust with people?
nosy ppl, ppl who hold grudges, ppl who talk crap, ppl who twist stories just to make them look good and you bad. etc i can go on
Most relationships irregardless of whether or not there personal, people like to get over on you. When I was in school I heard everyone calling each other bestfriend but talk to another person about how fake there friend was. People suck nowadays. I guess you could trust them if you joined a bleeding fellowship that never left the room. I hope this girl im going to start dating doesnt lie as much as the girls before.
when someone isn't there when you really need them. Say you're down and out, depressed, kinda hint towards it to your supposed best friend and they do nothing to go out of their way to make you happy... yeah that definitely affects trust for me (just happened recently in case ya can't tell!)
it takes alot (maybe too much but what will do it everytime is when a 'friend' goes around making me look bad, being a hater