What is the ruling on using phrases such as "What does Shaykh Ibn 'Uthaymeen have?" or "Shaykh Ibn Baz has come to you" or "Lighten up, Ibn al-Qayyim," in response to advice, whether these phrases are said in jest or in seriousness?

Mocking people is forbidden, especially those who speak about knowledge, advising their brethren, whether in jest or seriously. This is based on the Almighty's saying: "O you who have believed, let not a people ridicule [another] people; perhaps they may be better than them; nor let women ridicule [other] women; perhaps they may be better than them." Mockery is the belittling and ridiculing of people, and the one being belittled might be greater in stature with Allah. Mocking those who adhere to Allah's religion and implement His commands contains a type of hypocrisy. If they are mocking them because of the Sharia, then their mockery of the Sharia is disbelief (kufr). However, if they are mocking their persons regardless of their adherence to the Sunnah, then they are in grave danger.