A' fellows, Jock and the laird.
"Spoken when unworthy fellows intrude themselves into the company of their betters."—Kelly.
A fey man and a cursour fearna the deil.
Meaning literally, that a predestined man and a war-horse (or stallion, as the word "cursour" more immediately implies) fear not the devil.
Affront your friend in daffin', and tine him in earnest.
Affront him not in jest, lest you lose him in earnest.
A fidging mare should be weel girded.
"A thief does not always steal, but always be on your guard against him."—Russian.
A findsilly bairn gars his faither be hang'd.
A fisherman's walk—twa steps and overboard.