Adds the ability to jam cigarettes into the filter slot of a gas mask

code/game/objects/items/cigs_lighters.dm

@@ -322,9 +322,20 @@ CIGARETTE PACKETS ARE IN FANCY.DM
 		return
 	var/to_smoke = smoke_all ? (reagents.total_volume * (dragtime / smoketime)) : REAGENTS_METABOLISM
 	var/mob/living/carbon/smoker = loc
-	if(!istype(smoker) || src != smoker.wear_mask)
-		reagents.remove_any(to_smoke)
-		return
+	// These checks are a bit messy but at least they're fairly readable
+	// Check if the smoker is a carbon mob, since it needs to have wear_mask
+	if(!istype(smoker))
+		// If not, check if it's a gas mask
+		if(!istype(smoker, /obj/item/clothing/mask/gas))
+			reagents.remove_any(to_smoke)
+			return
+
+		smoker = smoker.loc
+
+		// If it is, check if that mask is on a carbon mob
+		if(!istype(smoker) || smoker.get_item_by_slot(ITEM_SLOT_MASK) != loc)
+			reagents.remove_any(to_smoke)
+			return
 
 	reagents.expose(smoker, INGEST, min(to_smoke / reagents.total_volume, 1))
 	var/obj/item/organ/internal/lungs/lungs = smoker.get_organ_slot(ORGAN_SLOT_LUNGS)

code/modules/clothing/masks/gasmask.dm

@@ -26,10 +26,17 @@ GLOBAL_LIST_INIT(clown_mask_options, list(
 	var/starting_filter_type = /obj/item/gas_filter
 	///Does the mask have an FOV?
 	var/has_fov = TRUE
+	///Cigarette in the mask
+	var/obj/item/clothing/mask/cigarette/cig
 
 /datum/armor/mask_gas
 	bio = 100
 
+/obj/item/clothing/mask/gas/worn_overlays(mutable_appearance/standing, isinhands)
+	. = ..()
+	if(!isinhands && cig)
+		. += cig.build_worn_icon(default_layer = FACEMASK_LAYER, default_icon_file = 'icons/mob/clothing/mask.dmi')
+
 /obj/item/clothing/mask/gas/Initialize(mapload)
 	. = ..()
 	init_fov()
@@ -45,15 +52,64 @@ GLOBAL_LIST_INIT(clown_mask_options, list(
 	QDEL_LAZYLIST(gas_filters)
 	return..()
 
+/obj/item/clothing/mask/gas/equipped(mob/equipee, slot)
+	cig?.equipped(equipee, slot)
+	return ..()
+
+/obj/item/clothing/mask/gas/adjustmask(mob/living/carbon/user)
+	if(isnull(cig))
+		return ..()
+	balloon_alert(user, "there's a cig in the way!")
+
+
 /obj/item/clothing/mask/gas/examine(mob/user)
 	. = ..()
-	if(max_filters > 0)
-		. += "<span class='notice'>[src] has [max_filters] slot\s for filters.</span>"
+	if(cig)
+		. += span_notice("There is a [cig.name] jammed into the filter slot.")
+	if(max_filters > 0 && !cig)
+		. += span_notice("[src] has [max_filters] slot\s for filters.")
 	if(LAZYLEN(gas_filters) > 0)
-		. += "<span class='notice'>Currently there [LAZYLEN(gas_filters) == 1 ? "is" : "are"] [LAZYLEN(gas_filters)] filter\s with [get_filter_durability()]% durability.</span>"
-		. += "<span class='notice'>The filters can be removed by right-clicking with an empty hand on [src].</span>"
+		. += span_notice("Currently there [LAZYLEN(gas_filters) == 1 ? "is" : "are"] [LAZYLEN(gas_filters)] filter\s with [get_filter_durability()]% durability.")
+		. += span_notice("The filters can be removed by right-clicking with an empty hand on [src].")
+
+/obj/item/clothing/mask/gas/Exited(atom/movable/gone)
+	. = ..()
+	if(gone == cig)
+		cig = null
+		if(ismob(loc))
+			var/mob/wearer = loc
+			wearer.update_worn_mask()
 
 /obj/item/clothing/mask/gas/attackby(obj/item/tool, mob/user)
+	var/valid_wearer = ismob(loc)
+	var/mob/wearer = loc
+	if(istype(tool, /obj/item/clothing/mask/cigarette))
+		if(flags_cover & MASKCOVERSMOUTH)
+			balloon_alert(user, "mask's mouth is covered!")
+			return ..()
+
+		if(max_filters <= 0 || cig)
+			balloon_alert(user, "can't hold that!")
+			return ..()
+
+		if(has_filter)
+			balloon_alert(user, "filters in the mask!")
+			return ..()
+
+		cig = tool
+		if(valid_wearer)
+			cig.equipped(loc, wearer.get_slot_by_item(cig))
+
+		cig.forceMove(src)
+		if(valid_wearer)
+			wearer.update_worn_mask()
+		return TRUE
+
+	if(cig)
+		var/cig_attackby = cig.attackby(tool, user)
+		if(valid_wearer)
+			wearer.update_worn_mask()
+		return cig_attackby
 	if(!istype(tool, /obj/item/gas_filter))
 		return ..()
 	if(LAZYLEN(gas_filters) >= max_filters)
@@ -65,6 +121,13 @@ GLOBAL_LIST_INIT(clown_mask_options, list(
 	return TRUE
 
 /obj/item/clothing/mask/gas/attack_hand_secondary(mob/user, list/modifiers)
+	if(cig)
+		user.put_in_hands(cig)
+		cig = null
+		if(ismob(loc))
+			var/mob/wearer = loc
+			wearer.update_worn_mask()
+		return SECONDARY_ATTACK_CANCEL_ATTACK_CHAIN
 	if(!has_filter || !max_filters)
 		return SECONDARY_ATTACK_CONTINUE_CHAIN
 	for(var/i in 1 to max_filters)