That's one reason so many public speakers have Hawai'ian shirts. Women can also wear monster-high heels, as it makes them easier to see (It's not a "sexy" thing; it's a "see me" thing. There are some very conservative women's shoes, with very high heels).
I'm not a particularly good public speaker (but I've done a fair bit -why is everyone asleep?), so I need all the help I can get. I have a number of them.
I have a friend that has a .sig that says "Speak softly, and wear a loud shirt."
He has a lot of loud shirts.