The idiom "feel like something/doing something" is used in an informal way both in American and British English. When you have a wish, desire or inclination for something, you can use it in a normal way. It's nothing to do with politeness or impolitenesss. Besides, its use in the form of a question is seldom. The usual and polite way for offers and invitations is using "would" such as "Would you like a coffee?" or "What would you like to drink?" or "Would you have dinner with me tomorrow?".
I don't mean that you can not say "Do you feel like some coffee?" There is nothing wrong with it grammatically. What I mean is that we use this idiom in an ordinary way. It's just like when you ask somebody "Are you in the mood for dancing?"
It's a normal way of speaking.
Addressing your specific questions:
'Can you imagine how dirty it gets over time?'
When people talk informally, they are often a little sloppy. The present tense would be the perfect choice to state a generalization or natural law such as:
'White gets dirty over time.'
This idea was close enough for the speaker. Someone who likes to be more precise might say, instead, "Can you imagine how dirty it would get over time [if we bought the white pillow]?" But you might not enjoy living with someone who uses English precisely all the time. Such people tend to be nitpicky.
'The grease from your fingers will burn into the bulb and then it breaks.'
Here, two ideas have been spliced together into one sentence.
First idea: "[If you touch the bulb with your fingers] the grease from your fingers will burn into the bulb."
Second idea: "When that happens, i.e. when you touch the bulb with your fingers, the bulb breaks."
This is another example of the simple present being used for a generalization or natural law. And again, in a situation of informal speech you caught the speaker being a little sloppy.
'I hope it goes away overnight.'
I don't know how the English grammar experts would view this (if you want to know, you could ask over at ELU SE), but I will share how I see this example. My other primary language is Spanish, which has a subjunctive. English has one too, but people don't think about it much. In Spanish you really can't get away without thinking about it. In Spanish, this would be
Espero que se quite para mañana. ("se quite" is conjugated in the subjunctive)
I see the English sentence the same way -- I see goes away as the present subjunctive, which happens to be conjugated the same as the simple present.
Your questions were good, and you've done some careful listening and recording of what you've heard.
I would be remiss if I didn't point out a small but important misuse of the simple present tense in your question:
You wrote: I moved from Germany to California and since I'm here I hear people use the simple present....
Expressions beginning with "since" are notoriously easy to get tripped up on.
Better: I moved from Germany to California and since I've been here I've heard people use the simple present....
Or: I'm from Germany. Here in California I hear people use the simple present....
Best Answer
I believe the most appropriate phrase would be:
That is, you look like a person who catfishes.
The sentence "You look like a catfish" just makes me think someone is being compared to an actual catfish, likely as commentary about their mouth or facial hair.
If you want to use the verb, a "-y" or "-ey" suffix is typically added to make the verb into an adjective.
"You look catfishy" could also be a pun, as "[noun] looks fishy" or "[noun] smells fishy" is a very common saying that means something seems deceitful.