Assalaamu alaykum, if someone says something bad or does not like a sunnah and does not know that it is a sunnah, is this kufr (disbelief) or a sin? For example, a person does not like honey.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

Firstly, you should know that ignorance is one of the impediments to obligation (and, accordingly, to accountability in Islamic Law). When the Muslim denies anything of the sharee'ah out of ignorance, then he shall not be held accountable for it; he is not to be declared a disbeliever nor does he bear a sin for it. Ibn ʻUthaymeen wrote:

“Among the impediments to obligation are ignorance, forgetfulness and coercion; the Prophet, sallallaahu ʻalayhi wa sallam, said, 'Allaah has forgiven my nation their mistakes and forgetfulness, and what they are forced to do under duress.' [Ibn Maajah and Al-Bayhaqi] This is supported by texts in the Quran and Sunnah. Whenever the Muslim commits a prohibited act while being ignorant of the relevant prohibition, he bears no sin for it.”

As for disliking honey, the Islamic sharee'ah does not oblige Muslims to like honey, nor does it command them to like it; rather, the sharee'ah underlined that honey is a remedy. It has been narrated on the authority of ʻAa’ishah that the Prophet, sallallaahu ʻalayhi wa sallam, used to love sweets and honey. [Al-Bukhari and Muslim] What can be ultimately inferred from this report is that it is recommended to like these types of food.

It has been narrated that Anas said, “I saw the Prophet, sallallaahu ʻalayhi wa sallam, picking the pieces of gourd from around the dish, and since then I have kept on liking gourd.” [Al-Bukhari and Muslim]

Al-Nawawi commented on the lessons deduced from this hadeeth, “It is deduced from this hadeeth that it is recommended to love gourd and all that which the Prophet, sallallaahu ʻalayhi wa sallam, used to love.”

In brief, there is nothing wrong with disliking honey nor does it constitute going against the sharee'ah in the slightest.

Allaah knows best.