dowdy
One of the other guests at the table was a dowdily dressed middle-aged man.
I don't want to offend you, but why do you dress so dowdily?
She was dowdily dressed in black with an ugly grey hat on her head.
They were all bespectacled and dowdily clad in muted colours.
I can't see any reason for him to dress so dowdily.

SMART Vocabulary: related words and phrases

Not attractive to look at
back end
be no oil paintingidiom
be not much to look atidiom
bleakly
bleakness
gracelessly
have a face like the back end of a busidiom
hideous
hideousness
homeliness
putridly
reptilian
scrappily
scrappy
stolid
unpretty
unshapely
unsightly
vulgarity
vulgarly