For several decades, the standard method of measuring personality has been through self-report questionnaires. In this work, we apply a model based on the analysis of the words used by people. Using Machine Learning (ML) and Natural Language Processing (NLP) techniques, we created a classifier that categorizes people into their Myers-Briggs Type Indicator (MBTI) personality type based on text samples extracted from their social media comments. Then, we applied this classifier to determine the MBTI personality types of YouTube users who comment on videos related to conspiracy theories, spirituality, and travel. The results highlight that a sufficient estimate can be made with only 100 words per user, as long as all 100 words are related to the same topic. The most common MBTI type among YouTubers who comment on these types of videos is INFP, followed by INTP, INFJ, and INTJ, indicating a predominance of Introverted and Intuitive individuals. While the predominant personality type in YouTuber comments on videos related to conspiracy theories is INTP, in spiritual and travel topics, the most common personality type is INFP.