Jeta is kind of slang for a funny or ugly face.
Has visto la jeta de ese tío? Vaya careto más gracioso.
Note that tener jeta can also mean, "to have a nerve". The actual expression would be
ser un caradura or
tener la cara dura, and from that
cara the word
jetacan be used.
Has visto la jeta de ese tío? Se acaba de colar en la fila!
Second, the first performer is addressing the queen as de tú while the second, the guitarist, is addressing the queen as usted, which leads to other misunderstandings (if I recall correctly, the first one is the king himself talking to his beloved, while the second is the poor guitarist that has to put into music the king's passionate words... So the king can address her as de tú while the other musician can't, and that is made explicit at the beginning of the performance).
The poem goes:
Cuando (tú) miras con desdén, (tú) pareces fría, sujeta.
you look cold, restrained, and addresses the queen as de tú. The second guitarist starts with:
Cuando (usted) mira con desdén, parece (usted) fría ...
and then he has to stop because the
sujeta could be understood as
su jeta (su careto), and he could be telling the queen that her funny face looks cold.