What's the ugliest line of R code that still parses?
72 96 characters.

`c`&lt;-function(...){list(...)[[-1]];}-&gt;&gt;`c`;`[`=0;`]`=10;c(c,c)(c,c)(c,invisible)(`[`[]:`]`[])[];


Ugliness:


Reusing a standard function name
Using symbols as variable names
Global assignment
Right assignment
Self-redefinition of function
Unnecessary trailing semicolon(s)
Unnecessary sub-scripting numbers
Unnecessary quoting of variable name
Leaves the workspace in a state which will almost certainly break any subsequent code run


Generates the sequence 0-10 (thanks to Andrie for the idea to do that).

output:

 [1]  0  1  2  3  4  5  6  7  8  9 10