IM Etiquette

How to you explain to your son, who is only eleven and learning how to do short cuts on the computer that “cum” is not an acceptable short cut for come?

Can [friend] cum? He IM’s me this morning.

Mind you, I am in my office, he is in the back room. We are about four feet apart.

Come, I write back.

Mom, u r so old

This is his response to me when he feels I am clueless to current culture.

BEN, I type back, some short cuts aren’t short cuts.

Well, can [she] cum?

Give me strength.