regex string
\b[nl]+[\W_]{0,3}[!i\/?1\\]+[\W_]{0,3}[qgb]+[\W_]{0,3}[qgb]?[\W_]{0,3}(?:[e3][\W_]{0,3}r|a)(?!ia|al)s*\b

Test strings (matching)
nigga
n.i.g.g.a
n.i.g.g.e.r
n i g g a
Fuck NIGGERS
LIGGER
l\igger!!
n\gger
n/gger
niqqa
nibba
n1gger
N!gger!
nigge_r

L I B E R A L

non matching strings
LiviusMagnus
liberll
liberalism
linger
lifebringer
lighsaber
living alone
nibbler
nibbla
nibble
nigburgers
nicaragua
Night
Nigeria
Ligume
Legislation
My leg!
Nice work, Gary!
Tonight
Light
lighter
liberal
Danzig
Konnigsberg
Jigger
Pepperoni Germs

Uppity Nig

Trey Lorezno says, "Can.I g-ger a soda?"