Simulations of zero-thickness self-gravitating disks composed of gas clouds and stars presented here show that cloud-cloud collisions play a key role in throwing clouds out of the disk plane. The clouds then scatter stars, which under the influence of the halo/disk potential end up forming a bulge. This process can account for the presence of bulges in relatively isolated disk galaxies, which could have also acquired bulges via satellite capture at an earlier epoch. But, since satellites do not seem so abundant, some kind of internal process must produce, or help produce, bulges. Based on these results, cloud-star scattering seems a very viable candidate.