No, not because of the meaning, but because it sounds unfriendly.
"Ditto" is not slang. It is a perfectly good English word with a respectable Latin derivation ("dictus.")
Because "ditto" means "the same words as before," if person A says "Nice to meet you," if person B says "ditto," it is the exactly same thing as if person B spoke the words "Nice to meet you." When person B says it, "you" refers to person A, so when person B says "ditto," it means "I, person B, am pleased to meet you, person A."
The problem is that "ditto" is used to avoid effort and therefore suggests a lack of enthusiasm.
"Ditto marks" are quotation marks, used in lists to mean "the same as the item above."
One might imagine people ordering in a restaurant, and it turns out that everyone wants the same thing--the first diner says "I'll have the chicken cacciatore special," the next say "I'll have the same," and the next says "ditto" because he doesn't even want to make the effort of saying "I'll have the same."
Here's a correct example of the use of "ditto." Suppose someone keeping a record of the weather every day. They might write:
October 12th: Partly cloudy
October 13th: "
October 14th: "
The marks for October 13th and 14th, in this context, are "ditto marks" and would be read aloud as "ditto." They mean that the weather on October 13th and 14th as also partly cloudy.