I've found being aggressively assertive works well for me at times.
I think it's compensating for points when I was a youth. Back then I didn't really stand for my ground that well, and now it's about doing what I can or shold have done.
There are couple of instances lately where I have done this. the first was when I was seeing the new James Bond film. The worker there was giving out free ice creams for everybody who bought a ticket, and was moving down the queue before the film started. She missed me out, but didn't ignore the people immediately in front and behind me. I just let her have it and I shouted at her, and I didn't care how it looked. She looked at me really shocked, but i didn't care. she was deliberately trying to embarrass me when I didn't do anything wrong at all. I was a paying customer, and she deserved everything she got. I dont' care if it was unkind - was it? being "unkind" is arbitrarily denying somebody a service somebody is legally entitled to. If a person orders food in a restaurant, and they don't get the order, this is unethical. It's just basic business ethics and legality.
I feel better doing this, since it means I stand up for myself better.