I have always heard this but never thought about it... Until now. Apparently, if you have a small penis, you are a bottom.
Check out the info:
The research, titled “The Association between Penis Size and Sexual Health among Men Who Have Sex with Men,” began in 2006 and surveyed 1,065 gay men. Among its key findings: Those gay men who felt they had small or inadequate penis sizes were more likely to become “bottoms,” or anal receptive, while gay men with larger penises were more likely to identify themselves as “tops,” or anal insertive.
Another discovery from the research: men with smaller penises were more likely to be psychologically troubled than those with larger genitalia. The goal of the study was to understand the “real individual-level consequences of living in a penis-centered society.”