The phrase "am big on" is often used to express enthusiasm or passion for something. However, there are plenty of antonyms that suggest the opposite. For example, "am small on" suggests hesitation or apathy towards a particular issue. Similarly, phrases such as "am indifferent to," "am uninterested in," or "am ambivalent about" all indicate a lack of enthusiasm or interest. Other antonyms might include "am repelled by," "am averse to," or "am disinterested in." When trying to express the opposite of "am big on," there are a variety of words and phrases that can be employed to convey a range of different attitudes and emotions.