I guess slime people are now live.

code/game/objects/items/weapons/clown_items.dm

@@ -13,6 +13,8 @@
 		var/mob/M =	AM
 		if (istype(M, /mob/living/carbon/human) && (isobj(M:shoes) && M:shoes.flags&NOSLIP))
 			return
+		if(istype(M, /mob/living/carbon/human) && M:species.bodyflags & FEET_NOSLIP)
+			return
 
 		M.stop_pulling()
 		M << "\blue You slipped on the [name]!"

code/game/objects/items/weapons/grenades/clowngrenade.dm

@@ -69,7 +69,7 @@
 			var/mob/living/M = AM
 			if(ishuman(M))
 				if(isobj(M:shoes))
-					if(M:shoes.flags&NOSLIP)
+					if((M:shoes.flags&NOSLIP) || (M:species.bodyflags & FEET_NOSLIP))
 						return
 				else
 					M << "\red Your feet feel like they're on fire!"