I think this is one of the major fears that the partners of a lot of guys have - especially around whether T will make the person more aggressive. However, every time I've seen this question come up, the majority of the responses say that T has made the guy more at ease with themselves, more laid back, and better able to deal with life in general. There's always a few people who say that yes, their anger and aggression levels have risen, but that always seems to be the minority.
From a personal point of view, T has definitely made me feel much more at ease with myself. Quite a few of my friends have commented on this - how much happier I seem in myself. They've also said that I've become more assertive - not aggressive, but less likely to keep quiet about things that annoy or upset me. One friend has said that I've become more bossy - but in her eyes, bossy is a definite positive, so that's also a compliment - and I think she's probably referring to assertiveness as well.
Dave