Fix an antag rolling exploit

code/modules/mob/mob_helpers.dm

@@ -641,5 +641,26 @@ var/list/intents = list(INTENT_HELP,INTENT_DISARM,INTENT_GRAB,INTENT_HARM)
 	// Cast to 1/0
 	return !!(client.prefs.toggles & toggleflag)
 
+// Used to make sure that a player has a valid job preference setup, used to knock players out of eligibility for anything if their prefs don't make sense.
+// A "valid job preference setup" in this situation means at least having one job set to low, or not having "return to lobby" enabled
+// Prevents "antag rolling" by setting antag prefs on, all jobs to never, and "return to lobby if preferences not availible"
+// Doing so would previously allow you to roll for antag, then send you back to lobby if you didn't get an antag role
+// This also does some admin notification and logging as well
+/mob/proc/has_valid_preferences()
+	if(!client)
+		return FALSE //Not sure how this would get run without the mob having a client, but let's just be safe.
+	if(client.prefs.alternate_option != RETURN_TO_LOBBY)
+		return TRUE
+	// If they have antags enabled, they're potentially doing this on purpose instead of by accident. Notify admins if so.
+	var/has_antags = FALSE
+	if(client.prefs.be_special.len > 0)
+		has_antags = TRUE
+	if(!client.prefs.check_any_job())
+		to_chat(src, "<span class='danger'>You have no jobs enabled, along with return to lobby if job is unavailable. This makes you ineligible for any round start role, please update your job preferences.</span>")
+		if(has_antags)
+			log_admin("[src.ckey] just got booted back to lobby with no jobs, but antags enabled.")
+			message_admins("[src.ckey] just got booted back to lobby with no jobs enabled, but antag rolling enabled. Likely antag rolling abuse.")
+		return FALSE //This is the only case someone should actually be completely blocked from antag rolling as well
+	return TRUE
 
 #define isterrorspider(A) (istype((A), /mob/living/simple_animal/hostile/poison/terror_spider))