Big Man Syndrome (BMS) is marked by delusions that because there's a girl willing to sleep with you and hang on your every word (hence being a "big man") that everyone else, particularly males, are equally enthusiastic supporters of the mindless bullshit you purport. Other symptoms include: unwillingness to listen or compromise, unreasonable demands you expect to be fulfilled and the belief everyone else shares your interests.
"Man, Sean won't shut the fuck up. Ever since he started dating what's-her-face he's had some serious big man syndrome."
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