  We prove that a bounded operator $T$ on a separable Banach space $X$
satisfying a strong form of the Frequent Hypercyclicity Criterion (which
implies in particular that the operator is universal in the sense of Glasner
and Weiss) admits frequently hypercyclic vectors with irregularly visiting
orbits, i.e. vectors $x\in X$ such that the set $\mathcal{N}_T(x,U)=\{n\ge
1\,;\,T^{n}x\in U\}$ of return times of $x$ into $U$ under the action of $T$
has positive lower density for every non-empty open set $U\subseteq X$, but
there exists a non-empty open set $U_0\subseteq X$ such that $\nt{x}{U_0}$ has
no density.
