Looking back, I don't like my old answer so I'm adding a totally different answer.
A specific (theoretical) example of endothermic bond formation is described in Prediction of a Metastable Helium Compound: HHeF J. Am. Chem. Soc. 2000, 122, 6289-6290.
As reported in table 2:
The energy to dissociate HHeF to H + He + F is negative.
The energy to dissociate HNeF to H + Ne + F is negative.
The energy to dissociate HHeF to HF + He is negative.
The energy to dissociate HNeF to HF + Ne is negative.
However, HHeF is stabilized by being in a potential energy well, the activation energy to dissociate being relative high.
The authors conclude: "Remarkably, HHeF is also predicted to be a metastable species, which represents the first neutral compound containing a helium chemical bond."
The bond formation is endothermic.