Intro
Your reply isn't rude, but your reply doesn't match the tone of the message you recieved. Since this is your brother then it would typically be standard to reply back using conversation that aligns more with restricted code over elaborated code.
Restricted code
This is speech that is dependant on context, relying on the shared understanding between an in-group. This type of language reflects familarity and is typically considered "warm". This also allows for less verbose speech for easier and faster communication.
For example this was a past text message conversation between me and a roommate (male,platonic)(certain details removed to protect identities/privacy). This is an example of a question and answer using restricted code:
roommate: Can u go in the draw on my desk the long one pause and get the <restaurant> menu
me: Cant send images to <phone brand/model>
roommate: I just need the number to them
me: <phone number>
roommate: Preciate it
As can be seen in this conversation there are almost no formalities used except at the end of the request. Text is economical, providing exactly the information needed. It sounds like a conversation would sound.
Other parts represented in this type of speech are use of written asides/jokes:
long one pause
And use of Eye Dialect
Preciate it
Elaborated code
This is speech that is not dependant on context and can be understand by anyone regardless of whether they are in-group or out-group. The point of this speech is to ensure understanding, but is rarely used between family members.
For example, this is a text conversation using elaborated code between me and a job recruiter (details removed to protect identity/privacy).
recruiter: Hello Maximilian, this is <Recruitor's Name> with <Company1>. I received your application for the position of <job>. Are you still interested in this position? [...]
My apologies. I accepted a position at another company.
No worries. Thank you for responding.
As you can see this conversation has a liberal use of formalities and can be understand without almost any context needed. The conversation is obviously between two strangers and there is not a shared upon agreement for lexicon, dialect, tone, etc to be used. Since there is no context for this conversation it will be as general as possible to ensure the maximum amount of people may understand what is being said and as well as being as curteous as possible to minimize chance of offendending.
The Question Directed At You (Restricted Code)
The text you recieved uses similar level of restricted code in comparison with my first example:
Come get some strudel
The meaning of this is completely dependant on the shared context between you and your brother. It matches the level of restricted code typically seen in English between people of the same family, and may be a little more concise than spoken word because of the medium (text).
Your Reponse To This Question (Elaborated Code)
Your reply on the other hand utilizies more elaborated code than restricted code:
Thank you, but I don't feel like eating strudel right now
Not only does this create dissonance in tone of the conversation due to the mismatch of code used, it also may even convey a level of distance in how you view your relationship with your brother. Examples of why this is elaborated speech include: use of the character ,
, verbose phrase usage "thank you" rather than "thanks".
I am going to elaborated though more specifically about a particularly dissonate detail in your reply:
I don't feel like eating strudel right now
This is an elaboration that is verbose since the context with what you want to do with said strudel is understood and does not need to be said, the example of this phrase in restricted language would be:
I don't feel like strudel right now
This would not effect tone much if not for how it also works to avoid use of mimicry in regards to verb usage, the question was
get some Strudel
The response elaborates needlessly and inserts verb that is different and more clear to the restricted code use of get some
.
Reply That Matches Restricted Code
I do not know the exact relationship you have with your brother, however since he initiated with the first message using a liberal amount of restricted code and since he is a direct family member, I would assume you would want to reply back in restricted code and with the same type of tone.
There are many ways to say this and it will depend on your relationship and shared lexicon/ dialect between you and your brother, however the words thanks
and good
are generally what the main words should be in your reply (in most circumstances).
I think the reply that would best fit in this circumstance would be:
Nah im good
This is a phrase I use liberally and have never been called rude when I use it in informal situations that warrant restricted code.
Linked as well is the urban dictionary entry for "nah im good", which has 91 upvotes and 10 downvotes with the first definition being:
A casual way of saying "No thanks"
However, if that is not your style then here are a few more examples that may work:
Im good
, Im good thanks
, Im good thanks though
Thanks but im good
Im fine right now
Nah im good for right now
Not feeling strudel rn
Nah im not feeling strudel rn
Nah im chillin
Further Reading