If the traffic is backed up for a stoplight, you shouldn't have any trouble keeping up. Merge and take the lane. Make sure you're far enough left in the lane for oncoming left-turning traffic to see you. If you're keeping up there's no reason for anyone to be unhappy with you. Just don't cut in line.

Sometimes a driver will come up on the left and try to pass or cut you off in this situation. Don't let them freak you out, keep a lid on your temper, and you'll be fine.