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mad, dippy, stupid, silly, eccentric not right in the head or mental. Can be either positive or negative.
1. That girl is so dappy, I tell you. But ya gotta love her She's got a lot of nerve 2 go out wiv a black bloke round ere!(good)

2. That girl is so dappy. She will never see any sense, what a totally unsuitable guy to go out with. She will pay the price for her dappiness.
by rach February 26, 2003
Dappy is one third of the group N-Dubz.
N-Dubz are from London.

He wears woollen hats.
Dappy - Na-na-na it's N-Dubz
by JetPie December 12, 2007
Used to descripe a girl who is a bit dippy but also a bit mad or eccentric. Friendly mild insult.
Emily: So I locked my housekey in my locker again..
Jas: Your so dappy!
by Last Chancer October 22, 2006
dappy is a term usually associated with certain types of girl. sometimes the person in question may be mad, loony, or in my own experience, a complete nutter.
that kirsten is dappy as fuck
by chaz April 15, 2004
Doing something stupid and/or uneccisary.
Tom: I broke my arm on my trampoline

Louie: Your so dappy!
by Morsli June 05, 2009
A person that acts cool when they aren't or is unnecessarily loud in a public place.
John: you see that guy over there shouting at random people and acting like he's cool?

Steve: yeah, he's such a dappy
by deirdre barlow 69 January 24, 2013
a despicable or disgusting person
A: I raped your sister...

B: you Dappy cunt
by jnojones October 12, 2011