The slaadi could be utterly capricious, fighting one moment and parleying the next. Or, as in my campaign, they just like to fight, attacking viciously for a few rounds before backing off and retreating if the opponent is notably stronger. Since slaadi heal easily, they use these random battles to establish their territory in Limbo. But since other creatures don't heal as easily, they tend to kill their potential competitors without meaning to.
Since the slaad's life cycles are reliant on violence, most slaadi are self-serving and paranoid, making sure that their battles are for territory only and that they aren't turned into breeding shells for red slaad eggs. This makes them seem more evil than not to humanoids.
In addition, the slaadi are also caught up in a war of attrition with the githzerai. Both the lawful gith race and the chaotic slaadi view each other as a threat to their existance, so slaadi are likely to attack humanoids if they feel the least bit threatened.
Also, most slaadi view structures as an affront, as permanency of any kind is so scarce on Limbo. Thus, they tend to destroy objects without some use of destruction (like weaponry- most slaadi shun armor).
Just my two cents.
Demiurge out.