One or two common(ish) unrelated assumptions that really bother me

Assumption #1:

If someone is bisexual they have to be with both men and women.

I've come across a fair few people that are under the impression that it is impossible for someone who identifies as bisexual to be faithful. For example, if a bisexual woman is married to a man, she would be unable to be faithful to him as she has to be with a woman as well. This is so incorrect it's not even funny. Being bisexual simply means being attracted to both genders. They are no more likely to be unfaithful than straight or homosexual people. The only difference it makes is that they have the potential to be attracted to both males and females as opposed to just one or the other. For example, there are billions of women out there that have the potential to be attractive to me. However, this does not mean I will cheat because I have this amazing thing called self control which allows me to be faithful to Laura. If I turned out to be bisexual, this would not change.

Assumption #2

How can we know (enter topic here) happened if it was meant to have happened before humans were alive.

SCIENCE MOTHERFUCKERS!!! I wouldn't dream of attempting to explain exactly how we are able to know about things that happened before humans were around, I sadly don't possess much knowledge of advanced science. However, there are various techniques of approximating events that happened long, long ago that have been developed over the years. Sure, they're not entirely accurate and could end up being completely wrong. This is why scientists tend to say they think something happened. But just because there were no humans around at the time, or the event wasn't recorded doesn't mean it didn't happen. What really bothers me is when Christians use this argument. There's no way there were humans around when God (allegedly) said "Let there be light", yet people who believe in the Bible are rather certain it happened. Yay for contradictory statements!

Assumption #3

The ocean can't be rising due to global warming because the icebergs are already in the ocean.

Yeah, I've actually heard that one. One word: glaciers.