"Let their table become a snare before them: and that which should have been for their welfare, let it become a trap." (Psl.69:22)
Something given for our welfare, says David, is capable of becoming, instead, a pernicious trap. In this Psalm, he reminds God of the wrongs done to him by his enemies then suggests ways the Almighty might employ to avenge him. And this is his first recommendation: "Let his table become a snare to him." Let his means of sustenance become a means of sabotage. Who would deny that food and/or drink have been the downfall of more than one person? There are those whose health has been impaired, whose lives have been cut short, or even ruined, by either what they have eaten or drunk or how much they have consumed.
Other things come to mind, as well, that fall into the category of blessings capable of morphing into curses. For instance, the gift of sex can be so twisted and abused that all its intimate beauty is turned into salacious ugliness. Not only that, friends who should be a joy and help to us can become tools of the devil to lead us astray from God. Then there is government, that which God surely meant for our welfare, but which has, unfortunately, morphed into a body of all-knowing, intrusive “benefactors.” And, contrary to what you may think, service to God can be a snare, if it becomes a substitute for fellowship with Him, since it can leave one especially unsuspecting of sin.
These were only the first four that came to mind immediately. There are many others you could add to the list, now that I've gotten you to thinking; which, incidentally, is what I meant to do. Ask God to show you if there is a blessing in your own life in danger of becoming a curse. It is such a destructive possibility that David chose to wish it upon his worst enemies.
Blessings and curses sometimes dress alike; so look deeper.