present participle of disappoint
"The rain made our picnic plans disappointing, so we had to stay indoors and watch movies instead."
In plain English: To disappoint is to let someone down by not meeting their expectations or hopes.
"The rain disappointed our plans for a picnic by forcing us to stay inside all day."
not up to expectations
"a disappointing performance from one who had seemed so promising"
Causing disappointment.
"The disappointing result left everyone feeling let down after weeks of hard work."