goof 
(gf) Informal
(gf) Informal n.
1.
a. A playful, silly, or outlandish person.
b. An incompetent, foolish, or stupid person.
2. A careless mistake; a slip.
v. goofed, goof·ing, goofs
v.intr.
1. To make a silly mistake; blunder: goofed up by turning right instead of left.
2. To waste or kill time: goofed around at the mall.
3. To tease or make fun of someone: goofed on her younger brother.
v.tr.
To spoil, as through clumsiness; bungle. Usually used with up: goof up a job.
[Possibly alteration of dialectal goff, fool, from obsolete French goffe, stupid.]