"Bastard" doesn't necessarily mean that the person being told that is bad, it is just a claim about his origin.
"I will fuck you" means that the speaker is sexually attracted to the person being told that.
"Bastard" doesn't necessarily mean that the person being told that is bad, it is just a claim about his origin.
"I will fuck you" means that the speaker is sexually attracted to the person being told that.
"Bastard" is a bad word because it is almost always used as an insult. It is almost always used to disparage somebody. There are some contexts where this word (and other insults) are accepted, for example if a young man says about his friend that the friend is "a cool bastard". Here, an actual insult is used to sound "cool" or "edgy". But this use can be very tricky for non-native speakers, so it's better to just not use insults.
Why is "bastard" almost always considered to be an insult? Because over a large portion of history and in many cultures, being a "bastard" was considered something bad. A "bastard" is an offspring from a relationship that is considered less valuable, maybe from a relationship that is considered altogether "illegitimate" (just this way of saying it tells a lot). So if you called somebody a "bastard", you actually said that this person is of lower value. This is almost automatically an insult.
Considering "fuck", this word for sexual intercourse it simply very rude. With many things, you can use words that are more polite, or words that are more rude. With some things, rude words are considered especially glaring. Sex and intimacy are among those. So you probably want to be extra polite, extra indirect with those topics, to not to step on people's toes.
Regarding
"I will fuck you" means that the speaker is sexually attracted to the person being told that.
that's so much simplified that it's basically wrong. "I will fuck you" is on the one hand really rude and impolite. On the other hand, it's stated as a fact. Consider the difference between
I will eat this cake.
and
I would like to eat this cake.
With "I will fuck you", you're not stating a wish or a request, but a fact. That could easily be read as an announcement of rape. If you said "I would like to fuck you", it would be a little better, but still considered quite rude. And it would probably still not cause the desired result ;) As I said, with sex and intimacy you want to be extra, extra, extra careful.
A word's origin is not the right way to determine wether a word is offensive or not, but instead, the right way is to check how socially accepted that word is. And if you still insist on saying a currently bad word, no matter how much you convince the person being told that it isn't bad in its origin, it would still remain unacceptable by him/her.
"Fuck" means emotionless sex, it is like rape.