Ecclesiastes 10:1 ~
Wise King Solomon himself weakened his own witness and weakened Israel by his folly of having so many wives and concubines.
A little joking and jesting, a clever remark, a witty saying ... all these mannerisms DETRACT from the serious deportment needed by a serious man or woman of GOD.
Is our mind ~ and hence, our conversation, our mode of behavior ~ upon Heavenly things? Or rather, do we carry of primary importance our clever and witty "interaction" with others ?
Are we bold and insistent with the sales clerks at the stores or in the shops ? Is our voice less than moderate so that others BESIDES the one we are addressing have to hear our concerns too ?
And never forget: a somber demeanor is helped by somber dress. Quiet colors and dark solids carry more weight in witnessing than loud and sassy and fashionable garments. Modest clothing, not form-fitting nor revealing , carries more weight in witnessing, also.
A covering on the head of women who are dressed in dresses ( or ample skirts or jumpers), long pants and long sleeves for men, go a long way towards somber dressing befitting a visible Christian witness.
Here is a rule of thumb:
When in public, if no-one EVER has come up to you when you are by yourself and asked you to pray for his or her concerns or his/her loved ones... then this is likely true: your public demeanor and dress are OUT OF LINE with Scriptures. You are not bearing a visible witness to CHRIST JESUS.
No-one recognizes you for being a Christian, alas ! Your visible witness as separated unto CHRIST JESUS has vanished, replaced with only a witness for Self... like the rest of the public.