Team meetings -- especially gatherings such as brainstorming sessions -- are supposed to be a non-judgmental place to freely express ideas and get the ball rolling. But if all of your contributions are met with derision, scorn and dismissals from your boss then you know something is amiss. If you're being ignored or -- even worse -- "shushed" during the creative process, then that's a problem that needs to be addressed immediately.
SOLUTION: We sound like a broken record at this point, but you need to talk to your boss about this. Some bosses just aren't great with people or social skills, and he/she honestly might not even realize it's happening. This is a tough tightrope for an employee to walk because if you come across as a complainer, then you're just going to be viewed as a whiner. So eat some humble pie and try something along the lines of "I feel like I might not be expressing myself in meetings in the most effective way and I definitely have a lot of good ideas I'd like to communicate. Do you have any tips that might help me and, in turn, benefit the team?"
There's room to be smart and savvy without turning into a total pushover. Find that middle ground.