Approach colloquial expressions with caution. It’s fine to say whaddup in an email but definitely not fine to say whaddup or even what’s up in an academic paper. Also, note that profanities should be avoided in formal writing, as should slang.

The inclusion of the occasional bit of slang works well in some articles and papers, but exercise caution. High school teachers are not likely to approve of slang-addled papers, and colloquialisms would be out of place in certain articles or papers. It’s safest to avoid the issue altogether by writing bright, colorful, but formal prose.