In Duke Nukem: Manhattan Project, it can be seen that G.L.O.P.P. (Gluon Liquid Omega-Phased Plasma) mutates alligators, rats, pigs etc. into giant monsters. But, when I (Duke) am attacked with green-colored GLOPP by some monsters, only my health point is affected and I don't see any sign of mutation. Why? Duke doesn't wear any kind of armor to protect his DNA from exposure.
I asked the co-creator of Duke Nukem; George Broussard this question on twitter.
His response is simply that Duke is too badass to mutate.
Q : "I'm struggling to work out why Duke isn't mutated by his own GLOPP gun. Any ideas?"
A : "You can't mutate [a] bad motherf*cker.