Not to discourage any further discussion on the subject (as there is always more to say), but here are some previous threads that may address your question:
How Truly Incompetent was the Italian Military by u/Klesk_vs_Xaero
Why was the Italian Military so Incompetent? by u/Smoked_Peasant
Why was the Italian Military so Pathetically Inept? (User deleted).
The bad reputation mostly comes from World War II, where many factors were at play.
Regarding Ethiopia, if you mean the first attempted invasion (in 1896) I would like to point out that unlike people randomly say, the Ethiopians of 1896 weren't natives fighting with spears and swords - they had 100,000 rifles and dozens of artillery pieces. The defeat of Adwa had largely political reasons; an expeditionary force of less than 20,000 Italians and Askaris had been sent against an Ethiopian army of some 100,000 men, in a terrain that the Ethiopians knew well and the Italians did not. General Baratieri, the Italian commander, was well aware of this and had adopted what one could call a 'Fabian strategy' which was working well enough, but the government at home was impatient for a decisive victory and pushed him to attack against unfavorable odds. It should also be pointed out that this was far from being the only European defeat at the hands of Africans in that era - one may mention the battles of Isandlwana, Khartoum, El Herri, Annual. The difference was that unlike the UK, France or Spain, Italy did not strike back, and signed a treaty recognizing the independence of Ethiopia; again, this lack of reaction was largely due to the internal condition of Italy in the late 1890s (social upheaval, governments falling in succession, the 1898 Milan riots followed by the assassination of the king in 1900...)
The second invasion of Ethiopia (in 1936) resulted in the conquest of a country twice as big (in terms of surface) as France in little more than a year, inflicting over 300,000 casualties on the Ethiopian armed forces while suffering between 3,000 and 10,000.