The tag alias #77275 pens -> pen is pending approval.

Reason: Plural to singular.

The singular tag form (pen) is not meant to be confused with pen_(artwork) according to the wiki page.

This one has a caveat that pens is a common typo of penis. You can see this in the current search results for pens and even more so in the tag history. It's not enough to :| this alias for me, but it's something to be aware of and consider if there's an alternate route. I'm loathe to suggest adding even more disambiguations, but this may be a case where it could be warranted due to the frequency of mistags.