Mock Spraying-- HELP!

My youngest cat, Gizmo (he's 4) has been, what I can best describe as, "Mock Spraying." He doesn't do this when I'm the only one home, it's only around my sister (who, he makes crystal clear, he loves the most).

She'll sit on the couch, alone or sometimes when I'm there, watching TV and he'll begin this Mock Spraying behavior, where he goes to soft surfaces around the house and assumes the spraying position but doesn't actually emit any fluids. If he is disrupted during this time he gets very aggressive, hissing and growling, and will not stop until he's either removed from the surface or until he has "finished". Tonight, he's been particularly tenacious in his insistence of his Mock Spraying.

If this was the sole behavior, we wouldn't be terribly concerned, a little weirded out, but not looking for action except that he has, a couple times, also urinated while exhibiting this behavior (literally on myself and my sister, usually while we were crashed on the couch sleeping). I don't think I need to tell anyone how traumatic being urinated on in your sleep is, so we're looking to find a way to put a stop to the behavior. I think I forgot to mention that he has been neutered, a couple of years ago. Does anyone have any pointers/tips? Is this indicative of a bigger underlying issues (medical, perhaps) or is it kitty teenage angst?

I'd like to add that he doesn't necessarily do it in specific places, pretty much all over the house and, short of covering my house in vinegar, I really don't know what to do. He's been doing it approximately every 10 - 20 minutes tonight.

I do have another cat, Beau, who I've had longer than Gizmo; he has IBS (irritable bowel syndrome) and often has flare ups of vomiting. So we have been paying more attention to Beau recently as he's just coming off a particularly bad flare up.

Again, I'm at a loss and could really use advice!

I know they usually squat and pee when there is a UTI, but it's not unheard of for spraying to be indicative of a problem. I would definitely have him checked out by a vet, especially if he's doing it every 10-20 minutes. Is anything coming out while he's "mocking" this evening? He could be getting blocked, which is extremely serious. (I know, not what you want to hear late at night)

If you have seen pee come out of him tonight, either in a litter box or on a vertical surface, then probably you could wait until tomorrow to call a vet. But if you have not seen him pee normally, and he's doing this so often, and getting upset and aggressive, you may want to call an emergency vet. I've had a cat get blocked, and it's VERY painful for them, and dangerous as well.

Keep us posted.

Thanks for the input, I'll call the vet tomorrow. There doesn't appear to be anything coming out, but I don't think it's a UTI... he stopped the behavior immediately after my sister went to bed but it's better to be safe than sorry. I'll keep an eye out on him after he eats, he usually uses the litter box after eating.

He's acting really weird, though... He growled at my sister when she got up to go to bed (even though he was on the next couch over) and then immediately jumped to the couch she was previously sitting on and began the mock spray/urine behavior.

Definitely taking him to the vet as soon as possible. He's begun vomiting and growls at anyone who comes near him.

Thanks again for your help!

Not peeing, or being able to, is serious. If you haven't called the vet yet tell them you suspect that he could be possibly blocked and not able to pee. If they don't get you in within a 2-3 hours/same day of your call then call another vet as that's something needing emergency care.

A good vet will make time for you, though, in such a situation.

The vomiting is not a good sign, with regard to blockage. I hope you got him in and he's being helped. Please let us know how he is.