Question:
Can someone come a nazir if he thinks about it
Answer:
A person cannot become a nazir simply by thinking about becoming a nazir. Becoming a nazir needs that the person made a statement, that clearly states that he wants to be a nazir, or in certain circumstances if he inferred it. However without any expression, he will not be a nazir.
Sources:
Nazir 1-1, Nedarim 1-1.