But the part, with all its dad-jean banalities, has found Carell in “Rooster,” a campus comedy premiering Sunday on HBO. It doesn’t demand much of him, but he doesn’t let himself coast; bringing to bear his amazing comic timing and touch, he makes quite a bit out of not a lot. His portrayal of Greg Russo, a writer of hacky thrillers who finds himself embroiled in the cultural and sexual politics of a small liberal-arts college, is thoroughly grounded but also funny in surprising, off-kilter ways. “Rooster” is a mess, but Carell is never less than entertaining in it.