Only three real answers. No one can know for certain they aren't an asshole because it's really the perception of others; and many may not be willing to tell you "You're an asshole." On the flip side, you CAN know for certain you are an asshole; simply knowingly being a jerk, arguing all the time and pissing people off.
An asshole, are you one?
I describe myself as a little dose of toxic masculinity.