I'll assume the nature of the emote isn't the problem, but then, could you please point me the issue(s) in my question  ?

I strongly disagree. There is a good chance your question was flagged due to the subject matter.

Or at least, advices to improve my question, if it was that bad.

Community users are asked not to engage in questions they don't believe are legitimate. We are asked to flag the question and allow a moderator to handle the situation. This is exactly what happen in your case.

I just got a question removed, without any comment or explanation.

A reason actually was given: This question was removed from Super User for reasons of moderation.

However, a moderator deleted the question, due to other users choosing to flag the question. Users with enough reputation are able to see which reason the moderator selected when the question was deleted: This question was marked as spam or rude or abusive and is therefore not shown

I told why I was needing it, and gave the (unsatisfying) results I found so far

You did not actually indicate the reason. However, not indicating the reason you need a specific emoticon, had nothing to do with the reason your question was deleted.

While I'm pretty sure no character is available ATM, I was expecting actual answer(s), with some information, or circumvention advices.

Every emoticon that exists is documented by the Unicode standard. If an emoticon does not exist there is a good chance it does not exist. You did not indicate what OS you were using, in general what emoticons exist on an OS, depends on what versions a specific OS support.

I'll assume the nature of the emote isn't the problem, but then, could you please point me the issue(s) in my question?

I strongly disagree. There is a good chance your question was flagged due to the subject matter. Common sense indicates that there isn't any legitimate use for emoticons that depict a body part or anything that violates a social normality. For instance, this is the reason emoticons don't exist, which have been used by hate groups (Nazi, KKK, etc.).

Or at least, advices to improve my question, if it was that bad.

Community users are asked not to engage in questions they don't believe are legitimate. We are asked to flag the question and allow a moderator to handle the situation. This is exactly what happen in your case.

I just got a question removed, without any comment or explanation.

A reason actually was given: This question was removed from Super User for reasons of moderation.

However, a moderator deleted the question, due to other users choosing to flag the question. Users with enough reputation are able to see which reason the moderator selected when the question was deleted: This question was marked as spam or rude or abusive and is therefore not shown

I told why I was needing it, and gave the (unsatisfying) results I found so far

You did not actually indicate the reason. However, not indicating the reason you need a specific emoticon, had nothing to do with the reason your question was deleted.

While I'm pretty sure no character is available ATM, I was expecting actual answer(s), with some information, or circumvention advices.

Every emoticon that exists is documented by the Unicode standard. If an emoticon does not exist there is a good chance it does not exist. You did not indicate what OS you were using, in general what emoticons exist on an OS, depends on what versions a specific OS support.