A sure-fire way to ruin the self-esteem of a cocky colleague is to hold the door open for him, say psychologists.
Such a gesture could be taken to imply that the recipient looks needy and vulnerable.
This is likely to clash with their masculine identity and leave them deflated, professors Janice Kelly and Megan McCarty of Purdue University in Indiana suggested.
Their study, published in the journal Social Influence, found no evidence that women were effected in a similar way when men held doors for them.
The authors said even fleeting examples of unexpected help can have significant impact if they work against typical gender roles.
Men who had the door held for them by another man reported lower feelings of self-esteem and self-belief than men who did not have the door held for them.
No differences were seen in women, regardless of whether a door was held open for them or not.