Does deathtouch from a creature deal lethal damage when it's blocked by multiple creatures?

Deathtouch means that any amount of damage that creature deals to another creature is enough to be considered lethal damage (CR 702.2b). This applies regardless of how many creatures are blocking it.

When a creature with deathtouch is blocked by multiple creatures, the attacking player must assign its combat damage in order among the blockers (CR 509.2). Normally, a creature must assign enough damage to a blocker to be considered lethal before moving on to the next — but because deathtouch makes even 1 damage lethal, the attacker only needs to assign 1 damage to each blocker before assigning damage to the next (CR 510.1c).

This means a creature with deathtouch and high enough power can effectively destroy an entire band of blockers, needing only 1 damage per creature to guarantee lethal damage on each of them.

Example: You attack with a 3/3 creature with deathtouch. Your opponent blocks with three 2/2 creatures. You can assign 1 damage to each of the three blockers. Since deathtouch makes 1 damage lethal, all three blockers will be destroyed after combat damage resolves — even though normally a 3/3 could only trade with one 2/2 at a time.

Note that the attacker still must assign at least 1 damage to a blocker before moving to the next in the declared order (CR 509.2). You cannot skip a blocker in the ordering entirely unless you assign it at least 1 damage (assuming it has at least 1 toughness).