9-high is the worst possible hand that can still win, as long as you have 3 or fewer opponents to beat at showdown.
Throughout this answer I'm just assuming that flushes are not considered; it is very easy to come up with a set of 9 cards where you don't have any 5 of the same suit.
Your hand: 2,6
Opponent hand: 2,5
Community cards: 3,4,7,8,9
Your best 5 for the showdown: 9,8,7,6,4
Opponent's best 5 for the showdown: 9,8,7,5,4
You win with the 9-high, 6 kicker.
This situation applies up to there being 4 people at showdown, since all 3 opponents could have the same hand.
Could your hand be any worse? No.
First off, 8-high is automatically an impossible hand to have. You have 7 available cards to make your hand, and if you cannot have any duplicates, then you'd need 7 distinct cards that are 8 or lower, and those only exist if the cards are 2-8. This means you'd actually have 4,5,6,7,8 for a straight.
So to look at possible worse hands of 9-high:
Of the 7 cards available to you, there are only 8 unique numbers from 2-9 to pick. If you leave 2 of those numbers out, then you only have 6 unique numbers to fill 7 slots, so by the pigeonhole principle you'd have at least a pair. Thus there is a single number left out. If that number were 2-4, then you'd have a 5-9 straight. If that number were 7-9, then you'd have a 2-5 straight. Thus the missing number must be either 5 or 6. This only leaves you with 2 possible sets of 7 cards:
- 2,3,4,6,7,8,9
- 2,3,4,5,7,8,9
If you have the first set, that is the solution proposed above. If you have the second set, that is what your opponent had. There is no other worse hand that can be made for 9,8,7,5,4 to beat.
There are other variants where you can switch the 2 with any of the community cards and still end up with the same result. All that matters is that you have a 6 while your opponent has a 5, and that the other card you have is the same as your opponent's other card.