Personally, it seriously irks me. Sometimes it offends me greatly, depending on the mood I'm in. It is always offputting and offensive in some way.

I think it's a problem with language reclamation and our community. The way that I see the world, trans people of all ilks (trans women, trans men, kings, queens, gender fucked folks, genderqueer folks etc.) all are part of the same community. We all have "deviant" gender experiences and we all are oppressed by society in similar ways.

That does not mean, however that the same language is used to marginalize us, or that the particulars of our cohort experiences are not different. For instance, trans man resources aren't helpful to me, because I'm a trans woman. Sure, there is a lot of overlap (changing documents and stuff) but transition resources and navigating privilege and how oppression manifests itself is very different for different cohorts of trans identities. It's not to say that anyone has it "worse" or "better", just that we all have different experiences around our trans identities because our identities are treated differently by society.

The word "tranny" (Kate Bornstein insists that its etymology comes from something positive in a trans woman and drag queen community in Australia in the '50s so we should all be all about using it) has become, regardless of where it came from, a word to hurt trans women. Occasionally, it is used in other cases, but do a google search. Look at the results. Look it up in "Urban Dictionary". You get a few things about automobile transmissions, and a whole bunch of really transphobic, transmisogynistic hate speech about trans women.

In our culture today, "tranny" is a word used to make jokes at the expense of trans women, and to illicit homophobic responses in cis, hetero, men when they check out a woman, stigmatize trans women, etc. It is targeted. It has a frightening amount of violence attached to it for being a word used for trans women for such a short amount of time, and it almost always targets trans women when used as a hate word.

That all said, I find that when trans men use the word "tranny" to describe themselves, or lightly, or as a catch-all community word, I get offended. I try not to get offended at language, but it's a word that targets trans women. It's not some cutesy fun word that is short for "transgender" or something. It's not just making "trans" feel more like a standalone word or more fun. It is a word that many trans women are deeply offended by and that has trauma, violence, murder, pain, and a lot of other oppression attached to it, and every time trans guys around me toss it around I feel a little less safe in that space, and a lot more excluded. Please, just, don't use it; I try not to, save very particular circumstances and with very particular people.