From the definition:

"Word History: Although we associate tulips with Holland, both the flower and its name originated in the Middle East, where both are associated with turbans. Tulips were brought to Europe in the 16th century; the word tulip, which earlier in English appeared in such forms as tulipa or tulipant, came to us by way of French tulipe and its obsolete form tulipan or by way of Modern Latin tulīpa, from Ottoman Turkish tülbend, "muslin, gauze." (Our word turban, first recorded in English in the 16th century, can also be traced to Ottoman Turkish tülbend.) The Turkish word for gauze, with which turbans can be wrapped, seems to have been used for the flower because a fully opened tulip was thought to resemble a turban."

http://www.sex-lexis.com/Sex-Dictionary/tulip

from New Partridge Dictionary of Slang and Unconventional English

male homo

Why not just that, litétally an "overdressed tulip" ?

Could fit well with "beau nasty" :

DGD / botanique :

nasty = nastie n. f.

Définition :

A tendency of a plant organ, such as a bud, petal, or leaf, to move in a direction determined especially by the nature and structure of the organ, rather than by external stimulus.

Here's a nice quote from a site that gives more info:
As Robert Anderson writes in “Spring: A Fragment,” from his Poems on Various Subjects, published in 1798,
How different seems the tulip, gaudy flow’r!
How gaily deck’d, yet priz’d but for its shew!
So shines the witless beau—vain, tinsell’d thing!—
That glides thro’ life unnotic’d but for dress.
http://www.erudit.org/revue/ron/2004/v/n36-37/011136ar.html

See also:
NETBible: fop
- [ Traduire cette page ]
fop, n. an affectedly elegant or fashionable man; a dandy. ... gaudy as a peacock, gaudy as a butterfly, gaudy as a tulip, flaunting, flashing, flaming, ...
net.bible.org/lexicon.php?word=fop

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Note added at 18 hrs (2008-07-27 10:40:39 GMT)
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Note to asker: As you suggested, the tulip is often referred to as a gaudy flower (although I find that rather unfair on most tulips), and that's the image when it's used for a person.

Perhaps tulip attributes originate from Tulip mania
http://en.wikipedia.org/wiki/Tulip_mania

denoting beauty, sudden richness, hence pretentiousness

We use it in slang like:
Why don’t you say so you tulip you; as in “fool” or
http://www.thefreedictionary.com/chucklehead
Informal
A stupid, gauche person; a blockhead

Or as already suggested overdressed fop