To me ‘show off’ is most irritating trait of any one.For girls specifically, it is ‘arrogance related to physical appearance’. Being aware of one’s ability (Beauty) is confidence.But making others aware of it always is arrogance.

Confidence must be like fragrance of flower and not like stink of gutter.

When it makes others happy,I call it confidence and when it make others disgusted, it becomes arrogance.

via What quality in others makes you want to slap them?