The point...

I assume we must be able to take knowledge with us, otherwise we'd arrive in 1818 without knowing we were from the future. Therefore, I'd convince them by describing the outcome of historical events then taking place as well as wowing scientists with my amazingly advanced understanding of things with which they were only just getting to grip. I'd also travel to Germany to meet Baron von Drais who patented the first bicycle that year (he called it a Laufmaschine, and he invented it because a the eruption of Mount Tambora in Indonesia had caused crop failures in what became known as "The Year Without A Summer" and people had to kill and eat their horses to avoid starvation) and tell him about chain drives and pedals, because it took another 50 years for anyone to think of that and make the bicycle useful.

Demonstrate some positions from the Kama Sutra lol

Ah. @Donotbelieve touches a good point. The differences and diminution of language would be another evidence. And scientific knowledge a little ahead of its time. Now I'm influential enough to really maim the space-time-flying-spaghetti-monster continuum.

Perhaps telling everyone that you are from the future may not be a good idea .

I'd just grab a guitar and start playing something.