If a person makes fun of another person for refusing to do things his parents forbade him to do and I laugh listening to this mockery, am I a kaafir by making fun of Islam? You should know that the name of God or Islam wasn’t mentioned in this conversation.
I don't see any reason that you are a kafir, but yes it is FISQ(mistake), and you should repent.
And next time as per the hadees, you should do as such:
On the authority of Abu Saeed al-Khudri (may Allah be pleased with him) who said: I heard the Messenger of Allah say, “Whoever of you sees an evil must then change it with his hand. If he is not able to do so, then [he must change it ] with his tongue. And if he is not able to do so, then [he must change it] with his heart. And that is the slightest [effect of] faith.” (Recorded in Muslim)
By this hadees, we can conclude that if someone doesn't even consider something evil in his heart, it means his faith is very weak.
But in your case, you have your regret now, and that's great, you should repent and focus on making your faith stronger. Believe in Allah and his mercy.