The sentence, "She said she gives the best head you can ask anybody," can be considered amusing or ironic due primarily to its double entendre, the play of words that has dual interpretations. The first interpretation is literal and innocent, implying that she gives the best advice or opinion, as "head" can symbolize wisdom or intellect. But the term "head" also has a slang connotation in a more sexual context. The humor originates from the tension between these two disparate interpretations.
The irony emerges from a situation where the woman is singing her praises unknowingly or naively about an ambiguous phrase that could be perceived in a far different, potentially embarrassing context by others. The humor appears when the listener knows both meanings. They are startled and amused by the stark contrast between the woman's probable innocent intention and the risqué implied connotation.
Cultural and generational gaps can add another layer to this irony. The sentence could portray a speaker who is unaware of the current, more risqué slang. The norm or expected behavior would be for that person to use contemporary slang appropriately to convey their intended message. However, the speaker does not follow the expectation which can be perceived as humorous or ironic because the speaker seems to believe they are saying something praise-worthy while it can be interpreted quite salaciously.
The sentence can also be considered funny because it's challenging to assess the validity of an implicitly subjective claim. It's amusing to think about one boasting about such a personal and intimate skill because it’s generally considered private, barely quantifiable, and not something usually discussed so openly, making it a humorous exaggeration or hyperbole to claim being the best.
On the flip side, if we consider she is intentionally using the sexual connotation, the irony then arises from the audacious and nonchalant claim to be "the best," it's also thumbing a nose at socially expected modesty and privacy around such topics. This sudden, bold proclamation could draw laughter from shock and surprise, not necessarily interpreting the sentence as something funny but reacting to the brazenness of it.
In the end, humor is highly subjective and hinges on societal, cultural, and personal interpretations. This sentence contains elements of surprise, shock, and defiance of norms, making it possible to be perceived as funny or ironic. Furthermore, it underlines the importance of understanding phrases' double meanings to prevent any unintentional amusement at our expense due to the misuse of language. She said she gives the best head you can ask anybody