No fighting urself

commands/games/tic-tac-toe.js

@@ -23,6 +23,7 @@ module.exports = class TicTacToeCommand extends Command {
 
 	async run(msg, args) { // eslint-disable-line complexity
 		const opponent = args.opponent || this.client.user;
+		if (opponent.id === msg.author.id) return msg.say('You may not play against yourself.');
 		if (this.playing.has(msg.channel.id)) return msg.say('Only one game may be occurring per channel.');
 		this.playing.add(msg.channel.id);
 		try {