When he gets pig-headed, even his dad can't do anything about it.
Tips
memory
Look at the character: 强 (strong) sitting on top of 牛 (ox / cow). A 'strong ox' - that is, an animal that won't budge no matter how hard you push. That's exactly what 犟 means as a personality trait.
register
犟 is colloquial and slightly negative. It overlaps with 固执 ('stubborn'), but 犟 is earthier - it's the word a frustrated parent or grandparent uses about a child who refuses to back down.
Bottom indexing radical 牛 - pictograph of an ox's horned head. The ox is the proverbial stubborn animal in Chinese folk imagery, dug-in and immovable when it decides not to budge. Pair the strength above with the ox below and the character draws itself: "as headstrong as a strong ox."
Top 强 supplies the sound - qiáng drifting to jiàng with a tone and onset shift. It also adds meaning: stubbornness is strength turned inward. The pairing is one of the more transparent semantic compounds in everyday Chinese - "a strong ox" reads almost literally as "pig-headed obstinacy."
