I don't think you two necessarily disagree.
One way to reconcile these ideas is to point out that it's entirely rational to push someone away you don't want to be with.
However, I think the grandparent comment is really talking about otherwise stable relationships where one party can, quite suddenly, start behaving very differently. Usually when this happens, someone will try to justify themself, saying that the reason is X or Y, often blaming the other party. E.g. they'll pick something close at hand, some bad habits or old points of conflict to justify the mood.
Consider two examples, with 'your' bad habit being leaving dirty dishes. If you just left a huge mess in the kitchen, an argument that evening is not irrational. If it happened earlier in the week without consequence (you cleaned up later), but suddenly it's being brought up as the cause of conflict, be suspicious that there's something else going on.
Honestly, sometimes when this happens to you, your relatively normal perception of the situation can make the really irrational stuff seem almost comical. However, it's so easy to get baited into an argument that that's what often happens. A little awareness and firmness in not getting drawn in can go a long way. There are patterns to recognize.
The key isn't to excuse irrational behavior (after all, the tailgater is still being dangerous), but to take it into account in how you respond. You can save yourself immense grief with half a second of realization that "something's up."