In the absence of your manager, your colleagues were acting irresponsible and neglecting all manager's direction. What will you do?

I will join that group of colleagues & will have a fun party then :D

I would take the lead and remind my subordinates that we have work to do. I would also fool them and say that we are being recorded :P  it always works....

1. Give him a word of advise

If it doesn't work ---

2. Remind him of the consequences

If it doesn't work ---

3. Report him to the management

Those things that i would do, unless there are pre-stated terms and policies in regard to any actions

Get their attention through a physical meeting, email or memo.

Open 'speech' with a small joke.

Speak to them about collective goals and aspirations

Remind them about the team's corporate goals and then the immediate objectives.

Encourage them, saying that when we win, each person wins.

Ask questions about their thoughts or personal challenges and obstacles in carrying out tasks

Re-strategize and re-delegate, based on feedback from above. Include my own tasks as well.

Put timelines to each person's task and milestones for success.

Document all and circulate the agreed to-do list.

Encourage action and regular feedback in case of difficulty or more challenges.

Circulate scorecard and achieved tasks to team by email.

Give full report of achieved tasks to manager by email or SMS.