1, The conversation went off at a tangent.

2, He never sticks to the point but keeps going off at a tangent.

3, One moment the professor is working hard on a problem in physics, the next he's gone off at a tangent and he's talking about bees.

4, It's hard to get a firm decision out of him - he's always going off at a tangent.

5, Let's stay with the topic and not go off at a tangent.

6, Loretta's mind went off at a tangent.