This sentence might be considered funny or ironic for various reasons and through the application of several angles of humor. One such reason is that it makes the recipient curious about the supposedly inappropriate content, despite there being none in the first place. The sentence itself is innocuous and perfectly ordinary, but the suggestion of inappropriate material can evoke an unexpected response. Knowing that there might be inappropriate content which is not directly referred to can pique curiosity, invite speculation, and result in unintended humor.
Another aspect of irony could be related to context. If this sentence is spoken or written in a situation where the reader would not normally expect any inappropriate content, it can be ironically funny. For instance, in a professional meeting or a formal setting where one would naturally expect appropriate language and topics, yet someone ironically mentions the presence of inappropriate content that can't be provided.
The sentence may also be seen as funny due to the straight-faced delivery of an arguably absurd statement. Humor regularly hinges on the unexpected or anomalous, and this phrase could qualify, especially when there's no apparent reason for the content to be inappropriate. The dry declaration could make it a perfect deadpan joke, leading to laughter from the surprise and absurdity.
The irony comes into play when the speaker is deemed to be a responsible person - ideally, a person who respects boundaries and avoids inappropriate content. Here, the reputable speaker apologizing for inappropriate content yet not providing it is a contradicting situation, a trait that breeds irony. The very person who should uphold appropriateness is indirectly linked to inappropriate content.
In the realm of meta-humor, where the joke is on the joke itself, this sentence could be viewed as a statement about the very act of application of censorship. Through stating the presence of inappropriate content, the sentence paradoxically initiates the censorship it refers to. In the act of remarking on inappropriate content, it draws attention to its existence while withholding its details, ironically purporting to shield the reader from said content.
Finally, the phrase could be read as a commentary on the often arbitrary determination of what counts as "inappropriate content". Often, the context and diverse cultural norms can dramatically shift the definition of 'inappropriate', leading to humorously contrasting interpretations. The sentence's usage raises questions about what it might contain, and why that might be viewed as inappropriate to some but not others. I'm sorry, I can't provide the text as it contains inappropriate content.