Is it possible to see two rainbows crossing each other, like an x?
Sure, if you have two suns.
There are a lot of interesting rainbow effects. I don’t know of rainbows crossing, but you can see two rainbows that meet. This happens if you have two rainbows – one due to the sun, and the other due to the reflection of the sun in, say, a lake. So you do have “two suns”, as Nametag suggests. They meet at the horizon, so unless you’re in an elevated position, you won’t see them cross.
Rainbows from nearby sources (two streetlamps, for instance) might be seen to cross.
For info on rainbows, see M. Minnaert’s The Nature of Light and Color in the Open Air, R.A.R. Tricker’s Introduction to Atmospheric Optics, Greenler’s Rainbows, Halos, and Glories, and Jearl D. Walker’s The Flying Circus of Physics. William B. Corliss’ Handbook of Unusual Phenomena lists a lot of anomalous rainbows, but take it with a grain of salt – some of hos “unexplained” phenomena have been explained long ago. Others are seeming errors, and others, tantalizingly, may be real or may be erroneous reports. There are also a lot of great photos on websites.
If the reflecting surface is horizontal, at least (like a lake). I’ve heard reports, though, of rainbows from all sorts of reflective surfaces, including the windows of a building. In that particular case, they were too far apart to cross, but one can imagine similar circumstances where they would
Perhaps if you had one caused by the direct rays of the sun and the other caused by a reflection (at a very shallow angle) off the side of a large glazed building.
It occurs to me that, even without reflection at odd angles from buildings or whatever, it’s still possible to have rainbows that cross. If you have a primary rainbow due to light from an image of the sun from a horizontal mirror behind you (like a still lake surface), it can meet and cross the secondary rainbow from the direct sunlight. There have been several reports, sketches, and pictures of such a reflected rainbow “connecting” the primary and secondary rainbows, but I’m not aware of any that cross the secondary. But it’s certainly possible.
Incidentally, even though the reflected rainbow has the same diameter as the unreflected bow, its unusual position and )often_ limited extent lead people to see it as straight, and people often report a straigh “rainbow pillar” rising from one foot of the non-reflected rainbow.