I am standing in a cue when I hear two people raising their voice at each other. My friend says to me 'one was being aggressive as she tried to push in' 'But - I replied- I heard her explain she was trying to catch up with her partner...' I guess you could look at this either way. Personally I think if she clearly and politely explained her need she was not being aggressive but rather assertive. The point is, sometimes we have a need that we are not prepared to compromise with although it may impact others. This happens especially at work but also in other circumstances. In those cases we will need to say clearly but politely what our needs are and how we feel about a certain situation. We also need to give the other person a chance to say ' their piece' and be prepared to discuss it. If however we raise our voice or react in a unfriendly manner, that becomes aggressive behaviour as we communicate to others that we do not value their ideas or their needs. The difference is quite clear to me and In the case above I believe to other observers too.