So what do you do as jungler when all 3 lanes are feeding?

Kick out one of your laners preferably a solo laner and say this is my lane now. Which means you only have 2 lanes feeding and a shitty jungler.

Alt f4, grab a gun and either shoot yourself or the screen.

There's a secret tactic for junglers. I don't know if you heard of it, I learned it from Nightblue3. Ready? The secret is...

to gank

Farm up and keep an eye out for possible capitalizations. Sometimes the enemy team will over extend or try a risky dive, just be ready for those, those are how you bring a lane back or get so strong yourself that you can sway the game on your own. Otherwise just keep up in farm and vision control then once the enemy team starts grouping just turtle and hope the other team screws up.

If not, then ff when you can, not every game is winnable.

Just camp bot and push to win.

Crawl into a corner and cry. Cry like you mean it. Cry like your life depends on it. Then next time all your lanes feed go bot early and play as 3 man bot.

You ff@20 and try a new game. Not all games are winnable.

Try ganking?

Bot lane might be the best to camp and crush when possible. You still have to gank intelligently but that will give your team the best opportunity to win. Because it will feed 3 champs and possibly net a dragon or 2. Communicate with the other laners that grouping and getting good grabs will lead to victory. You may still lose but its better than giving up.