KPD (Germany) in the late Weimar Republic (especially 1929-1933) acted and positioned itself in ways that made the Nazis and a significant portion of the population particularly反感 (dislike them). The main reasons are as follows:

Here are the most core points (in order of importance):

1. Violent street clashes and paramilitary activities: The KPD had its own paramilitary organization, the Red Front Fighters' Alliance, which frequently engaged in large-scale street brawls, shootouts, and riots with the Nazi SA.
Both sides attacked each other's rallies, tore down posters, and beat up each other's supporters, leading to nearly daily political violence on Germany's streets in the late Weimar period.
This caused many ordinary middle-class and conservative citizens to feel that social order was collapsing, and they viewed the KPD as extremist troublemakers sowing chaos.

2. Influenced by Stalin and the Comintern, the KPD regarded the Social Democratic Party (SPD, moderate left) as the "main enemy," labeling them "social fascists."
They refused to form a united front with the SPD against the Nazis, instead attacking the SPD as more dangerous than the Nazis.
This directly led to a split on the left: In 1932, cooperation between the KPD and SPD could have potentially prevented Hitler from coming to power. But the KPD's hardline stance allowed the Nazis to benefit.
Many centrists and SPD supporters came to deeply hate the KPD, believing they had "helped the Nazis."

3. Open advocacy of violent revolution and the dictatorship of the proletariat: The KPD openly called for the overthrow of the Weimar Republic and the establishment of a Soviet-style regime.
They supported the Soviet model, including confiscation of private property and class struggle, which greatly frightened the bourgeoisie, middle class, and peasants (fearing a "Russian-style terror").
During the Great Depression, they organized strikes, demonstrations, and even local armed conflicts, further exacerbating social unrest.

4. Viewed as "agents of Moscow": The KPD was completely subservient to the Comintern in Moscow and was widely seen as a "foreign-backed fifth column in Germany."
By that time, news of the Soviet Union's collectivization, Great Purge, and famines had gradually emerged, leading many to directly equate the KPD with "Bolshevik tyranny."
Nazi propaganda repeatedly emphasized the "Jewish-Bolshevik conspiracy," further amplifying this fear (although the proportion of Jews within the KPD was not particularly high).

5. Radical economic and cultural demands: They called for the complete abolition of capitalism, confiscation of large enterprises, land nationalization, and other extremist policies.
Culturally, they opposed traditional religion and family values, supporting radical sexual liberation, which also strongly repelled conservatives and the church.

Historical consequences: These actions allowed the Nazis to successfully portray the KPD as "the greatest threat to the nation," thereby gaining the support of the middle class and conservative forces.
After Hitler came to power, it is no surprise that the KPD became the first party to be banned and subjected to large-scale suppression.
In short: The KPD's extreme revolutionary stance + refusal to form alliances + street violence + pro-Soviet posture made it simultaneously offensive to the right wing (Nazis), centrists, moderate left, and ordinary people, ultimately becoming the greatest "political stepping stone" for the rise of the Nazis.
This is also an important lesson later reflected upon by many left-wing historians: Dogmatism and divisiveness helped fascism.