On Alfonso I of Portugal Wikipedia's page it says "In 1122, Alfonso turned fourteen, the adult age in the 12th century. He made himself a knight on his own account in the Cathedral of Zamora..." I have never heard of someone knighting themselves. Was it looked down upon at all?

First of all, Alfonso most likely didn't. But people did go about knighting themselves. At least if they were kings in Castile and Leon, just across the border, and precisely the kingdom that Portugal was breaking free from.

The first to do so would be either Fernando III, in 1219, or maybe even his father, Alfonso IX of Leon. The contemporary Chronica latina regum Castellae describes Fernando III taking his sword from the altar at the royal monastery of Huelgas outside of Burgos and strapping it around his waist. (His mum, Queen Berenguela, helped him adjust it, though. Those women).

Previously Castilian and Leonese kings would be given the crown and the sword by a bishop (starting with Alfonso VII in 1111 and 1124 in Compostela - we just don't have any evidence of royal knightings before him). The reasoning behind Fernando's break with tradition was now these kings thought it beneath them to be crowned and knighted by someone else, thus asserting their independence from any power, secular or ecclesiastic [1].

Interestingly, this must have been a peculiar Castilian/Spanish/Iberian thing. When Alfonso X knighted Prince Edward, the future Edward I of England, at Huelgas, the English guy did not think it was demeaning or degrading to have someone else hand you your sword (see Ruiz, p. 124).

There's a bizarre articulated statue of St James the Apostle, the so called [Santiago del Espaldarazo] (http://www.patrimonionacional.es/colecciones-reales/categorias/detalles/8558/Santiago%20del%20Espaldarazo/343), at Huelgas with a moveable right arm clutching a sword that was used in at least one of those royal ceremonies. (Actually, both arms and hands are moveable and have cords running through to set them in motion.) The king, as the tradition goes, thought it beneath his station to be knighted by someone else but the Apostle would do. The first instance that we know of was in 1332, to knight Alfonso XI. He took his armour and sword from the altar, put them on and then the statue gave him the necessary tap on the shoulder (or the cheek).

[María José Martínez estimates] (https://www.academia.edu/14732855/Las_imágenes_articuladas_en_las_celebraciones_aúlicas_el_Santiago_del_espaldarazo_de_Las_Huelgas_deBurgos) the statue was built on purpose for the 1332 coronation. Nevertheless, later some earlier kings would be said to have been knighted by said statue. Most notably, Alfonso X, even though in his case it is an early 18th century hoax by the Marquis of Mondéjar (see: Salvador Martínez H. Alfonso X, the Learned: A Biography, p. 101).

Further Reading

Clearly, there's a difference between self-coronation and self-knighting, even though the two were used in conjunction. I didn't really want to dwell on self-coronation here as this seems not to be what you're asking about. Just a couple of texts if anyone wants more food for thought. Both are available via Google Books.

Jaume Aurell, Strategies of Royal Self-fashioning: Iberian Kings’ Self-coronations, in: Self-Fashioning and Assumptions of Identity in Medieval and Early Modern Iberia, Leiden, 2015. Note that Aurell stresses that self-coronation was considered unorthodox and a transgression in the 12th century. The only recorded case in Castile would be that of Sancho II, who could be considered an usurper, not unlike Alfonso of Portugal, I hasten to add. It did become the accepted norm with a new ceremony elaborated for Alfonso XI and probably devised by the Portuguese.

Teofilo F. Ruiz, Unsacred Monarchy: The Kings of Castile in the Late Middle Ages, in: Rites of Power: Symbolism, Ritual, and Politics Since the Middle Ages, ed. Sean Wilentz, 1985. A good overview of different coronation ceremonies and practices in Asturias, Leon and Castile from the Visigothic times to the late Middle Ages. Just never mind him repeating time and again that the mechanic arm of St James was used to knight this or that king, you now know it's not true ))

As to knighting of Castilian kings, it is dealt with extensively by Bonifacio Palacios Martín in Investidura de armas de los reyes españoles en los siglos XII y XIII, available as a PDF [here] (http://gladius.revistas.csic.es/index.php/gladius/article/downlaod/112/113). He also mentions the case of Alfonso of Portugal (pp.190-191) but is somewhat incredulous. The Chronicon Lusitanum says that Alfonso knighted himself in 1125 at Zamora 'as was the custom of kings', even though that absolutely only became the custom 100 years later (and he hadn't even proclaimed himself king yet). Palacios thinks the chronicle in question was heavily edited in the next century when this scene was deliberately added in so as to give Portugal more prestige wrt other kingdoms.

[1] We are talking about kings who were knighted on their accession to the throne, as a lot of Castilian rulers were, becoming kings at a young age. In the rare event that the heir would come of age when his father was still alive, the king would knight the prince. Naturally, Alfonso of Portugal did not have a living father to do the honours. But he will knight his own son, the future Sancho I, himself in 1170 in Coimbra.