There's a scientific (and safe) way to do it.

Unplug from the mains, find the middle, remove that lamp, and test with a continuity tester, multimeter, or battery and bulb.

Test from one conductor to the mains plug, and one 'leg' will show open circuit. You have now eliminated half of the string from the problem.

Halve that 'leg', and remove that lamp. This test brings the process of elimination to 75%... on a set of 80, that's 60 lamps which don't need checking...

If you get continuity on both legs, it's the bulb in your hand with the fault...

Okay, it may be tricky to identify which 'leg' is which, but the 'lay' of the cable is a clue - the anti-clockwise leg is usually the left hand contact, etc...

Works for me, anyway. I rarely need to test more than 10 lamps on a set of 80.